Mitral valve dysplasia is a congenital malformation in the mitral valve complex which results in valvular insufficiency and regurgitation of blood through the valve annulus during systole. The defect leads to volume overload, volume expansion and often ultimately results in left sided congestive heart failure. Enlargement of the left atrium frequently acts as a substrate to trigger atrial fibrillation which increases the heart rate, decreases myocardial perfusion and further damages the heart. In the following report, diagnostic modalities including radiographic imaging, electrocardiography and echocardiography were used to make a diagnosis of mitral valve dysplasia with stenosis in a one year-old, Newfoundland. Medical therapy was instituted in an attempt to blunt the negative effects of the disease and prolong life.