Most reports of clinical experiences with palliation of acquired tricuspid regurgitation have failed to address the issue of coexisting disease of the mitral or aortic valve, or both. To accurately determine the natural history and the effect of operative interventions, we studied patients with chronic, pure mitral regurgitation who had surgical treatment at the National Heart, Lung, and Blood Institute from 1968 to 1984. Forty-seven patients fulfilled the criteria of a documented history of mitral regurgitation for more than 1.5 years, minimal mitral diastolic gradient, severe mitral regurgitation by angiography, and no prior mitral or tricuspid operative procedure. Twenty-five of the 47 patients (53%) had evidence of tricuspid regurgitation. No statistical differences in age, sex, mean duration of symptoms of congestive heart failure, or functional class were found between those patients with and those without tricuspid regurgitation. However, patients with symptoms of congestive heart failure for more than 6 years were more likely to have tricuspid regurgitation. This increased prevalence also correlated with higher elevations of left ventricular end-diastolic, systolic pulmonary artery, and mean right atrial pressures. The severity of tricuspid regurgitation estimated preoperatively did not correlate statistically with that determined by digital palpation, although the presence of tricuspid regurgitation was reliably confirmed. These data demonstrate that tricuspid regurgitation is frequently present in patients with chronic, pure mitral regurgitation and is associated with prolonged symptoms of congestive heart failure and significant alterations in right heart dynamics.