SummaryThe aim of the study was to assess the frequency of congenital heart defects in a population of dogs in Poland and to determine which breeds were affected by particular defects. A retrospective study of the medical records of cardiologically examined dogs revealed 301 cases of echocardiographically confirmed congenital heart defects. Dogs with congenital heart defects made up 2.7% of the dogs that underwent a cardiologic examination. The age at diagnosis ranged from 2 weeks to 190 months. Mixed breeds (33 dogs, 11%), Bull Terriers (31, 10%), Boxers (28, 9%), German Shepherds (17, 6%), Yorkshire Terriers (17, 6%), and French Bulldogs (16, 5%) were the most frequently affected breeds. Subaortic stenosis (120 cases, 33.9%), pulmonic stenosis (64, 18.1%), patent ductus arteriosus (59, 16.7%), mitral valve dysplasia (56, 15.8%), ventricular septal defect (24, 6.8%) and tricuspid valve dysplasia (17, 4.8%) were the most frequent congenital heart defects recognized in this study. Isolated congenital heart disease occurred in 258 dogs (86%), while multiple heart defects were noted in 43 dogs (14%). Most (60%) congenital heart defects were recognized in dogs older than 1 year. Early recognition of congenital heart defects is important for better patient care. Collecting information on the frequency of congenital heart defects in particular breeds will be useful in educating breeders and thus in improving the overall health of the breed.