ABSTRACTMitral incompetence in seven dogs ranging in age from 10 months to 5 years is described. The average age is 3 1/2 years. Clinical features are emphasized to facilitate recognition of the disease, which may have a higher incidence than thought previously. The condition is characterized by overt signs of left heart failure progressing to signs of right heart failure. Atrial fibrillation resulting from enlargement of the left atrium is a frequent feature and clinically is readily detectable. In particular, the prognosis in this series is very poor.