The development of late tricuspid regurgitation is an important complication of mitral valve surgery, as it is associated with a severe impairment of exercise capacity and a poor symptomatic outcome. The pathogenesis of this condition remains poorly defined, but it is usually attributable to a functional abnormality of the tricuspid valve. Whilst its development may indicate an increased afterload on the right heart as a consequence of persistent pulmonary hypertension, mitral prosthetic dysfunction, progressive aortic valve disease or left ventricular failure, late tricuspid regurgitation may also develop in the absence of these factors and then may reflect right ventricular dysfunction and/or a localized abnormality of the tricuspid anulus. Failure to recognize and correct tricuspid regurgitation at the time of initial surgery may also account for many cases of tricuspid regurgitation but its re-appearance following tricuspid annuloplasty is uncommon and usually reflects a failure of the mitral prosthesis. A reduction in the prevalence of late tricuspid regurgitation is an important objective in view of the high operative mortality and disappointing long term results associated with reoperation for tricuspid regurgitation. This may be best achieved through combining earlier mitral valve surgery with the accurate detection and liberal correction of accompanying tricuspid incompetence at the time of initial surgery.(ABSTRACT TRUNCATED AT 250 WORDS)