Management of patients with severe tricuspid regurgitation (TR) requires clarification of the mechanism of regurgitation. Primary disorders of the tricuspid valve, either congenital or acquired, may be identified by echocardiography. Severe TR often results from left-sided heart disease and secondary pulmonary hypertension. Cardiomyopathic processes may also cause right ventricular failure and functional TR. We report three patients with severe TR due to idiopathic annular dilation. The tricuspid valves were normal on surgical inspection, and pulmonary pressures not significantly elevated. Patients were aged over 65 years and had chronic atrial fibrillation with preserved left ventricular systolic function. Surgical treatment led to marked clinical improvement. Clinicians should recognize this unusual but treatable cause of right-sided congestive heart failure.