A 2-year-old female Maltese dog was referred with primary complaints of exercise intolerance and abnormal heart sound. Clinical and diagnostic investigation revealed split S2 and S4 gallop in the cardiac auscultation, tall P wave and left anterior fascicular block in the electrocardiogram, left atrial enlargement on the thoracic radiography, ostium primum atrial septal defect and cleft of the anterior leaflet of the mitral valve on the echocardiography. Based on those findings, the dog was diagnosed as the partial atrioventricular canal defect. Since the dog showed mild exercise intolerance, enalapril and furosemide were prescribed.