Patent Ductus Arteriosus (PDA)
and the Cavalier King Charles Spaniel

Patent ductus arteriosus (PDA) is the most common congenital cardiovascular abnormality in dogs. Cavalier King Charles spaniels have been shown to have a "high prevalence" for PDA.*

*See these veterinary journal articles regarding the prevalence of PDAs in CKCSs: September 2002, May 2003, November 2003, May 2011, November 2013.

PDA occurs when a temporary blood vessel – the arterial canal – which is used to bypass the fetus’s undeveloped lungs in the womb and allows blood to pass from the right side of the heart to the left, fails to seal within a couple of days after birth. Normally, this vessel will begin to seal once the pup begins breathing. PDA compromises the circulation of blood through the heart. It is believed to be inherited as a polygenic threshold trait with a high rate of heritability in some breeds and is considered to be hereditary in the CKCS.

Depending upon the size of the PDA, the excessive blood flow into the pulmonary artery can cause increased creation of pulmonary blood vessels, left atrial and left ventricular heart enlargement, and dilation of the aortic arch, due to an overload of the left heart. At the same time, the rest of the body is not getting adequate circulation. Development of aneurysms in the aorta is also common. Congestive heart failure, usually left sided but occasionally generalized, can develop as early as one week of age but may not occur until several years of age if the PDA is small.

Twice as many females are affected as males. If the PDA is not surgically repaired, the majority of dogs progress into left-sided congestive failure within a few years of life.



Many puppies will have no clinical signs of the effects of a PDA. If they do, typical symptoms include:

• Weight loss or failure to gain weight
• Difficulty breathing
• Coughing
• Exercise intolerance

 Many dogs have no clinical signs at the time of initial diagnosis.



PDA diagramA PDA is usually diagnosed at the puppy’s first visit to the veterinarian, who listens to its heart with a stethoscope (auscultation) and hearing a loud murmur as blood flows through the PDA. If the murmur is a continuous one, both during the the systolic and diastolic cycles of the heartbeat, then a PDA is suspected.

An x-ray (radiograph) of the heart likely would show an increased pulmonary vascular size and some generalized enlargement of the left side. An electrocardiogram  (EKG or ECG) would indicate left ventricular enlargement. The combination of auscultation, x-ray, and EKG should enable the veterinarian to classify the PDA as:

• Type 1: Small PDA
• Type 2: Medium PDA
• Type 3a: Large by pre-congestive heart failure (CHF)
• Type 3b: Large PDA plus CHF
• Type 4: Large plus pulmonary hypertension

The echocardiogram provides direct evidence for the presence of the PDA as well as permits evaluation of its consequences. The more sophisticated the model of echocardiograph device (e,g, color flow Doppler, spectral Doppler, transesophageal echocardiography (TEE), angiocardiography), the more information which the examining veterinarian will be able to acquire in order to assess how to repair the PDA.

Cardiac magnetic resonance imaging (cMRI) also has been found to be successful in identifying the morphology of PDA and the blood vessels surrounding the heart.



Closure of the PDA is strongly recommended for all dogs. Untreated dogs with a PDA are expected to have a 60% mortality in their first year.

PDA closure may be done by surgery or with a minimally-invasive Flipper Coilpercutaneous device”, inserted through a blood vessel. Surgery is the usual procedure for large PDAs or if the duct is tunnel-like. It is called a thoracotomy and involves inserting non-absorbable ligatures around the PDA duct.

PDA PlugThe minimally invasive procedures involve making a small incision in a hind leg and inserting into the artery a catheter containing a spring coil (for small PDAs), such as the Flipper (see photo at left), or a plug (for larger ones) such as the Amplatzer Canine Duct Occluder (ACDO) (see photo at right). The catheter is advanced into the aorta and the PDA, and the device is positioned into the PDA to stop the flow of blood through it.

Medicinal treatment following surgery, depending upon the extend of cardiac enlargement or heart failure, may include diuretics, ACE-inhibitors, and pimobendan.


Breeders' Responsibilities

PDA is considered a heritable disease, and therefore affected cavaliers should not be bred.


What You Can Do


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Veterinary Resources

Pulmonary artery lesions in Cavalier King Charles Spaniels. Karlstam, E.; Häggström, J.; Kvart, C.; Jönsson, L.; Michaelsson, M. Vet. Rec. June 2000;147(6):166-167. Quote: Postmortem samples from 7 Cavalier King Charles Spaniels (aged 8-9 years) that died or been killed because of problems associated with chronic valvular disease (CVD) were examined. The findings included mitral CVD and dilation of the left atrium and ventricle in all dogs, and left atrial rupture in two and severe pulmonary artery thrombosis in one. all dogs also showed wrinkling and irregularity of the endothelial surface of the main pulmonary artery and its branches. The pulmonary artery wall showed sever intimal thickening due to subendothelial fibrosis and abundant vacuolated, Alcian blue-PAS-positive intercellular substances compatible with glycosaminoglycans (GAGS). GAGS were also found in the tunica media. In more sever cases the internal elastic lamina, separating the tunica intima from the tunica media was fragmented and poorly discernible. It is suggested that CVD is part of a more generalised connective tissue diseases.

Patent Ductus Arteriosus Morphology, Pathogenesis, Types and Treatment. James W. Buchanan. J. Vet. Cardiol. May 2001;3(1):7-16. Quote: Patent ductus arteriosus (PDA) is the most common congenital cardiovascular abnormality in dogs. It represents persistence of the arterial canal that carries blood from the pulmonary artery to the aorta during fetal life and normally closes within hours after birth in response to increased oxygen tension. After birth, systemic pressure rises and pulmonary artery pressure falls so blood flow through a PDA typically goes from the aorta to the pulmonary artery (left-to-right flow) when the ductus fails to close. Depending upon PDA size, the added blood flow into the pulmonary artery causes increased pulmonary vascularity, left atrial and left ventricular enlargement and hypertrophy, and dilation of the aortic arch to the level of the PDA. A ductal aneurysm of the aorta is also common. Congestive heart failure, usually left sided but occasionally generalized, can develop as early as one week of age but may not occur until several years of age if the PDA is small. In some dogs with a large PDA, pulmonary hypertension sufficient to cause bi-directional or right-to-left flow exists. Histologic studies indicate that the pulmonary vascular disease associated with this type of PDA develops in the first month of life and the condition is essentially that of persistent fetal circulation.

Review of left-to-right shunting patent ductus arteriosus and short term outcome in 98 dogs. Van Israël N, French AT, Dukes-McEwan J, Corcoran BM. J. Small Anim. Pract. September 2002;43(9):395-400. Quote: The case records of 98 dogs [including nine cavalier King Charles spaniels] with a left-to-right shunting patent ductus arteriosus (PDA) were reviewed. There were 35 breeds represented, with a female to male ratio of 3:1. ... There were 35 breeds represented, the most common being German shepherd dogs (20 per cent), Cavalier King Charles spaniels (9 per cent), springer spaniels (8 per cent), crossbreeds (6 per cent) and border collies (5 per cent). ... The breed distribution in this study differed slightly from previous reports. Of particular interest was the apparently high prevalence of Cavalier King Charles spaniels in this group, although it was not possible to calculate the true incidence in the authors’ referral population. ... Forty per cent of the dogs were older than one year at initial presentation and 31 per cent had clinical signs attributable to PDA. A left heart base continuous murmur of grade IV/VI or higher was noted in 90 per cent of the dogs. On electrocardiography, the most common abnormalities were tall R waves (63 per cent) and deep QII waves (62 per cent). The radiographic triad of dilation of the descending aorta with enlargement of the main pulmonary artery segment and left atrium, typical of PDA, was noted in only 26 per cent of cases. Two-dimensional (2D) and M-mode echocardiography detected left atrial enlargement (35 per cent) and an increased left ventricular diameter in diastole (82 per cent) and systole (84 per cent) as the most common abnormalities. Doppler echocardiography demonstrated increased aortic outflow velocities in 66 per cent of cases. The overall short-term successful outcome in this study was 95 per cent. There was no significant difference between surgical ductal ligation using a standard technique or the Jackson-Henderson technique in terms of survival, occurrence of haemorrhage or residual shunting. The number of interventional procedures used in this study was too low for statistical comparison, but there appeared to be a trend towards a higher rate of residual shunting and a lower fatality rate using a coil occlusion technique.

Comparison of the incidence of residual shunting between two surgical techniques used for ligation of patent ductus arteriosus in the dog. Stanley BJ, Luis-Fuentes V, Darke PG. Vet. Surg. May 2003;32(3):231-237. Quote: Objective: To compare the incidence of residual patent ductus arteriosus (PDA) flow after ligation using 2 different dissection techniques: a standard dissection and a method described by Jackson and Henderson. Study Design: A randomized, prospective study. Animals: Thirty-five dogs admitted for surgical correction of a left to right shunting PDA [including five cavalier King Charles spaniels] Methods: Dogs were randomly assigned: 19 to a standard dissection technique (group S) [including three cavalier King Charles spaniels] and 16 to the Jackson and Henderson dissection group (group JH) [including two cavalier King Charles spaniels]. Results: Gender ratio, age at surgery, and diameter of the ductus were not statistically different between groups. Breed distribution was also similar. Because 1 dog had fatal intraoperative hemorrhage, only 34 dogs were available for residual flow comparisons. Twenty-one percent of group S dogs had residual flow compared with 53% in group JH. Whereas no intraoperative complications occurred in group S, 3 were encountered in group JH. Conclusions: The incidence of residual flow was higher when the Jackson and Henderson dissection was used for PDA ligation compared with a standard method of dissection. This was probably because of entrapment of loose connective tissue within the medial aspect of the ligature, impeding complete closure of the ductus. Clinical Relevance: Ideal PDA closure should result in no residual ductal flow to prevent possible adverse long-term sequelae, such as recanalization and infective endocarditis.

Patent Ductus Arteriosus in the older Dog. Van Israël N, French AT, Dukes-McEwan J, Welsh EM. J.Vet. Cardiol. May 2003;5(1):13-21. Quote: Objectives: The objectives of this study were to describe the clinical course of Patent Ductus Arteriosus (PDA) in older canine patients (defined as patients greater than 24 months at the time of presentation) with and without intervention. This study was also undertaken to evaluate if adult dogs with persistent flow across the ductus should still be closed, what the benefits are from late closure, and to hypothesise why some animals still continue to deteriorate despite closure. Background: Currently accepted therapies for patent ductus arteriosus are surgical ligation and transcatheter coil embolisation. The majority of dogs are diagnosed and treated at young age. Some older dogs survive with few clinical signs and live a normal life span without intervention. Some dogs deteriorate despite intervention. Methods: The case records of 24 dogs that had reached 24 months of age before diagnosis were reviewed and those animals that had no concurrent congenitaal cardiac diseases were included in the study (n = 21) [including two cavalier King Charles spaniels]. Those animals that were still alive were requested to participate in a long-term follow-up study. Results: After closure of the ductus (n = 16), the clinical signs disappeared in all but one animal. On follow-up of these animals, there was echocardiographic evidence of left ventricular systolic and diastolic dysfunction in many. Late cardiac death was recorded in 3 animals [including one cavalier King Charles spaniel]. In dogs where there was no intervention congestive heart failure was a common, but not an inevitable sequel. Development of mitral valve endocardiosis was a common feature. Conclusions: Older animals with PDA follow an individual course, independent of pre-existing heart failure. Irreversible left ventricular dysfunction is common, however it does not seem to affect the clinical course. These data show a favourable outcome in a high percentage of adult dogs diagnosed with PDA that undergo closure. Outcome without intervention was less favorable.

Long-term follow-up of dogs with patent ductus arteriosus. Van Israël N, Dukes-McEwan J, French AT. J. Small Anim. Prac. November 2003;44(1):480-490. Quote: Postocclusion survival data from dogs with left-to-right shunting patent ductus arteriosus (PDA) was available from 80 dogs [including eight cavalier King Charles spaniels], diagnosed from 1990 to 2000. ... The breed distribution, which included a high prevalence of Cavalier King Charles spaniels, was slightly different from that reported previously. However, it was a representative sample of the dog population with PDA. ... Of these, 37 had undergone a procedure to close the ductus and were re-evaluated at the time of this study; clinical data from the follow-up examination was compared with that from the original examination. Radiographically, the right ventricle remained apparently enlarged, and the aortic bulge associated with dilation of the descending aorta did not disappear after closure. On M-mode echocardiography, left ventricular chamber diameter in diastole and systole and left ventricular posterior wall in systole decreased significantly. Mitral endocardiosis was a common feature. Residual flow was evident in 46 per cent of the animals. Late closure occurred in 8 per cent of the dogs, and trivial recanalisation in 19 per cent. The maximum survival time postclosure was 168 months and, after non-occlusion, 114 months, suggesting that dogs with PDA follow an unpredictable course. However, there was a significant difference in survival times between the corrected and non-corrected group.

Use of simultaneous fluoroscopic and echocardiographic guidance during transarterial coil placement for embolization of patent ductus arteriosus in dogs. Viktor Szatmári, Arnold A. Stokhof. J. Am. Vet. Med. Assn. March 2006;228(6):881-884. Quote: Objective: To evaluate the use of simultaneous fluoroscopic and transthoracic echocardiographic guidance during transarterial coil placement for embolization of patent ductus arteriosus (PDA) in dogs. Design: Descriptive report. Animals: 3 dogs with PDA [inclulding a cavalier King Charles spaniel]. Procedure: Each dog was anesthetized, and a femoral artery was exposed for vascular access. By use of an introducer, a catheter was placed in the thoracic portion of the descending aorta with fluoroscopic guidance, and subsequently, a bolus of iodinated radiographic contrast material was injected to outline the ductus. Under fluoroscopic guidance, 1 coil was positioned in the ductus, but not released. Transthoracic echocardiography was used to ensure that 1 loop of the coil was located in the pulmonary artery. When > 1 loop or no loops were detected in the pulmonary artery, the coil was retrieved and repositioned; when 1 loop of the coil was detected in the pulmonary artery, the coil was detached. After catheter removal, the femoral artery was ligated and the wound was closed. Results: In all 3 dogs, successful embolization of the PDA was achieved. Echocardiography prevented unintentional pulmonary artery embolization in 1 dog and suboptimal coil placement in the other 2 dogs. Conclusions & Clinical Relevance: In addition to fluoroscopic control, transthoracic echocardiography appears to aid the appropriate positioning of a transarterial coil for treatment of PDA in dogs. Although transesophageal echocardiography would likely provide better images of the ductus, transthoracic echocardiography is a much cheaper, less specialized, and more widely available alternative.

Transcatheter embolisation of patent ductus arteriosus using an Amplatzer vascular plug in six dogs. Smith PJ, Martin MW. J. Small Anim. Pract. February 2007;48(2):80-6. Quote: Objectives: The objective of this study was to assess the feasibility of transcatheter embolisation of a patent ductus arteriosus using an Amplatzer vascular plug (Amplatzer Medical UK) in six dogs. ... Dog 1 was a 54 kg, five-month-old, entire male, cavalier King Charles spaniel. ... Methods: The Amplatzer vascular plug is a self-expandable, cylindrical device attached to a delivery cable. In all the dogs, the device was delivered transvenously. Successful device implantation was defined as firm anchorage of the device squarely within the distal part of the ductus arteriosus with no intra- or postoperative dislodgement. Successful occlusion of the ductus arteriosus occurred if a disappearance of the continuous murmur was achieved 24 hours after placement of the Amplatzer vascular plug. Results: The age of the dogs ranged from 16 weeks to 7.5 years. Their weights ranged from 2.9 to 27.6 kg (median 6 kg). Two dogs had congestive heart failure before embolisation. Successful device implantation was achieved in all dogs. Successful occlusion of the ductus arteriosus was achieved in four of the six dogs. Complications included mild lameness, residual shunting, and bruising and pruritus around the surgical wound site. At follow-up, two dogs had a continuous murmur and one required treatment for congestive heart failure. Clinical Significance: This technique may represent a clinically effective and less expensive alternative to the use of an Amplatzer duct occluder (Amplatzer Medical UK) in dogs with medium-sized patent ductus arteriosus. Further investigations are required to fully evaluate its efficacy and safety in various sizes and types of patent ductus arteriosus, and to determine the optimal device size in relation to the size of the ductus.

Evaluation of the efficacy and safety of coil occlusion for patent ductus arteriosus in dogs. Tanaka R, Soda A, Saida Y, Sugihara K, Takashima K, Shibazaki A, Yamane Y. J. Vet. Med. Sci. August 2007;69(8):857-859. Quote: We performed a retrospective study of 56 dogs [including three cavalier King Charles spaniels] with Patent Ductus Arteriosus (PDA) to evaluate the indications for and efficacy of transarterial PDA coil embolization. Transarterial PDA coil embolization was conducted in 37 cases (66.1%) and surgical ligation was conducted in 16 cases (28.6%). Three cases (5.4%) were diagnosed as pulmonary hypertension and were excluded from surgical intervention. Although coil dislodgement was observed in the pulmonary artery in one case, no death occurred during coil embolization or surgical ligation. Echocardiography showed that fractional shortening decreased from 35.4 +/- 6.8% to 30.2 +/- 5.9% (P<0.05) after transarterial PDA coil embolization. Although slight residual shunts were observed in 18 cases, transarterial PDA coil embolization was effective treatment of PDA.

Transvenous occlusion of patent ductus arteriosus in 56 consecutive dogs. Julie E. Blossom, Janice M. Bright, Leigh G. Griffiths. J. Vet. Cardiol. August 2010;12(2):75-84. Quote: Objective: Document safety and efficacy of transvenous catheter occlusion of patent ductus arteriosus (PDA) over a wide range of ductal and patient sizes. Animals, materials and methods: Retrospective study of fifty-six consecutive dogs referred to Colorado State University with diagnosis of PDA. All cases utilized the transvenous approach, via the femoral vein. Occlusion was achieved using a coil (Flipper™) in dogs with PDA minimal dimension of ≤4 mm. Amplatzer® duct occluder or Amplatzer® vascular plugs were used in dogs with PDA minimal dimension >4 mm, or if a coil was unstable following deployment. Results: Ductal occlusion was achieved using the transvenous route alone in 54/56 dogs (96.4%). Occlusion was achieved using detachable Flipper™ coils in 39/42 dogs (92.9%) in which coil occlusion was attempted, with 38/39 dogs (97.4%) requiring only a single coil. In 16 dogs, occlusion was achieved using an Amplatzer® duct occluder or vascular plug. Post-procedure residual ductal flow was absent or only mild in 36/39 (92.3%) dogs in which it was assessed. Procedural mortality rate was 1.7%, and major complication rate 7.0%. Conclusion: Transcatheter occlusion via a transvenous approach is a safe and effective method for treating PDA in dogs and is useful for small dogs (<2.5 kg).

Retrospective Review of Congenital Heart Disease in 976 Dogs. P. Oliveira, O. Domenech, J. Silva, S. Vannini, R. Bussadori, C. Bussadori. J. Vet. Intern. Med. May 2011;25(3):477-483. Quote: Background: Knowledge of epidemiology is important for recognition of cardiovascular malformations. Objective: Review the incidence of congenital heart defects in dogs in Italy and assess breed and sex predispositions. Animals: Nine hundred and seventy-six dogs diagnosed with congenital heart disease (CHD) of 4,480 dogs presented to Clinica Veterinaria Gran Sasso for cardiovascular examination from 1997 to 2010. Methods: A retrospective analysis of medical records regarding signalment, history, clinical examination, radiography, electrocardiography, echocardiography, angiography, and postmortem examination was performed. Breed and sex predisposition were assessed with the odds ratio test. Results: CHD was observed in 21.7% of cases. A total of 1,132 defects were observed with single defects in 832 cases (85%), 2 concurrent defects in 132 cases (14%), and 3 concurrent defects in 12 cases (1%). The most common defects were ... patent ductus arteriosus (20.9%) [including nine cavalier King Charles spaniels] ... Several breed and sex predispositions were identified. Conclusions & Clinical Relevance: The results of this study are in accordance with previous studies, with slight differences. The breed and sex predilections identified may be of value for the diagnosis and screening of CHD in dogs. Additionally, the relatively high percentage of concurrent heart defects emphasizes the importance of accurate and complete examinations for identification. Because these data are from a cardiology referral center, a bias may exist.

Transesophageal Echocardiography Guided Patent Ductus Arteriosus Occlusion with a Duct Occluder. J. Silva, O. Domenech, A. Mavropoulou, P. Oliveira, C. Locatelli, and C. Bussadori. J. Vet. Intern. Med. November 2013;27:1463-1470. Quote: Background: Angiography and fluoroscopy are the standard methods to guide transcatheter occlusion of patent ductus arteriosus (PDA). The use of iodinated contrast agents and radiation exposure pose risks of animals and staff. Objectives: To assess feasibility of transesophageal echocardiography (TEE) for device size selection and procedure monitoring for PDA occlusion with a duct occluder (DO) without the use of angiography. Animals: Eighty client-owned dogs with left-to-right PDA [including four cavalier King Charles spaniels]. Methods: Prospective study. Dogs with left-to-right PDA undergoing transcatheter occlusion were included. Procedures were performed without angiography and device size selection was based on TEE measurements. Procedures were monitored with simultaneous TEE and fluoroscopy and both methods were compared. Visualization of the ductus and dimensions obtained by TEE and transthoracic echocardiography (TTE) were compared. Results: Complete PDA occlusion was achieved in 79/80 cases. TEE was consistently superior to TTE for PDA visualization and the latter showed higher values for ductal dimensions when compared to the former. TEE provided adequate procedure monitoring in 73 cases (91%). Fluoroscopy exposure time (2.77  1.2 minutes (mean, SD)) was lower than previously reported for the same procedure. Conclusions and Clinical Importance: TEE is a useful and efficient tool for device size selection and can be used for procedure monitoring in most cases. Fluoroscopy exposure time can be reduced and the use of contrast agents can be avoided. However, fluoroscopy is required in a minority of cases when TEE monitoring is not feasible or incomplete and should be available for this procedure.

Echocardiographic Assessment of Cardiac Function by Conventional and Speckle-Tracking Echocardiography in Dogs with Patent Ductus Arteriosus. I. Spalla, C. Locatelli, A.M. Zanaboni, P. Brambilla, C. Bussadori. J. Vet. Int. Med. May 2016;30(3):706-713. Quote: Background: Patent ductus arteriosus (PDA) is one of the most common congenital heart defects in dogs. Advanced echocardiographic techniques such as speckle-tracking echocardiography (STE) have not been extensively used to evaluate cardiac function in affected dogs. Hypothesis: Advanced echocardiographic techniques are more sensitive than standard echocardiographic techniques in analyzing systolic function in dogs with PDA. Animals: Forty-four client-owned dogs: 34 dogs with PDA (preoperative evaluation) and 10 healthy sex- and weight-matched controls. Methods: Prospective study. Dogs were recruited over a 2-year period. Complete echocardiographic evaluation was performed, including conventional (end-diastolic volumes indexed to body surface area in B and M-mode [EDVIB/M], end-systolic volumes indexed to body surface area in B and M-mode [ESVIB/M], allometric scaling in diastole and systole [AlloD/S], pulmonary flow to systemic flow [Qp/Qs], ejection fraction [EF] and fractional shortening [FS]) and speckle-tracking echocardiography ([STE]: global longitudinal, radial and circumferential strain [S] and strain rate [SR]). Results: Dogs with PDA had significantly different EDVIB/M, ESVIB/M, AlloD/S, Qp/Qs and all STE-derived parameters (global longitudinal S and SR, global circumferential S and SR, global radial S and SR)compared to healthy dogs. No correlation was found between standard techniques (EDVIB/M, ESVIB/M, AlloD/S, Qp/Qs) and STE-derived parameters (global longitudinal, circumferential and radial S and SR). Conclusion and Clinical Importance: Conventional parameters routinely used to assess systolic function (EF and FS) were not different between the groups; STE-derived parameters identified subtle changes in cardiac systolic function and contractility between the 2 groups of dogs. Based on these findings, STE may be a more appropriate tool to assess cardiac contractility in dogs with PDA.