Severe tricuspid regurgitation may produce significant morbidity and mortality if not corrected, but commonly used methods of intraoperative assessment may be unreliable. Tricuspid regurgitation was evaluated by a new intraoperative technique, Doppler color flow mapping, in 85 patients before and after cardiopulmonary bypass. Regurgitation grade by intraoperative color Doppler mapping correlated well with right ventricular angiography (kappa value = 0.92, p less than 0.01; n = 8) and with preoperative color Doppler studies (kappa = 0.71, p less than 0.05; n = 51). The right atrial V wave correlated poorly with the severity of tricuspid regurgitation intraoperatively, both before (r = 0.30) and after (r = -0.05, p = no significant difference) cardiopulmonary bypass. Advanced (3+ or 4+) tricuspid regurgitation was found in 40% (21) of 52 patients requiring mitral valve repair or replacement. Tricuspid annuloplasty with a prosthetic ring provided a significant (greater than or equal to 2 grade) reduction in regurgitation severity in 94% (17/18; p less than 0.05). Without repair, tricuspid regurgitation decreased to a similar degree after mitral valve operations in 14% (5/36); only one of the five patients had advanced tricuspid regurgitation prepump. Fluid filling of the arrested right ventricle after the surgical procedure did not predict regurgitation severity (false negative rate 50%, 2/4; false positive rate 22%, 2/9). Regurgitation grade remained unchanged after the initial postpump study, up to 60 weeks postoperatively. In conclusion, color Doppler flow mapping provides more accurate intraoperative assessment of tricuspid regurgitation than the right atrial V wave or fluid filling of the right ventricle. This semiquantitative technique aids in the selection of patients appropriate for surgical repair of the tricuspid valve and is useful in judging the adequacy of tricuspid valve repair before chest closure. Advanced (3+ or 4+) tricuspid regurgitation is a common occurrence in patients undergoing mitral valve repair or replacement and rarely responds to conservative (nonoperative) management. Ring annuloplasty provides a highly effective and durable reduction in tricuspid regurgitation.