Clinical and morphologic observations are described in 30 patients (23 [77%] of whom were in functional class III or IV) who underwent replacement of the mitral valve for mitral stenosis and either simultaneous replacement (13 patients, group I) or anuloplasty (17 patients, group II) of the tricuspid valve for pure tricuspid valve regurgitation. Comparison of the 13 patients in group I with the 17 patients in group II disclosed similar mean ages (55 vs 58 years), similar average preoperative right ventricular systolic pressures (64 vs 61 mm Hg), similar average right atrial mean pressures (10 vs 9 mm Hg), similar average left ventricular systolic pressures (126 vs 120 mm Hg), similar average pulmonary artery wedge-left ventricular mean diastolic pressures (16 vs 18 mm Hg), similar cardiac indexes (2.1 vs 2.0 liters/min/m2), similar mean heart weights (507 vs 535 g), and similar percents with grossly visible foci of left ventricular necrosis (15% vs 12%) and fibrosis (23% vs 12%). Of the 13 patients in group I, 10 (77%) died early (less than or equal to 60 days of tricuspid valve replacement) and 3 (23%) died late (29, 37 and 120 months); of the 17 patients in group II, 14 (82%) died early and 3 (18%) died late (4, 9 and 98 months). The causes of early death in the 2 groups were different: of the 10 patients in group I who died early, the cause was excessive bleeding in 5, low cardiac output of undetermined etiology in 3, dysfunction of both prostheses in 1 and cerebral insult in 1; of the 14 patients in group II who died early, none died from excessive bleeding, 4 from decreased cardiac output of uncertain cause, 5 from left ventricular inflow obstruction (produced by a Starr-Edwards ball-valve prosthesis in 4 and from a Starr-Edwards disc prosthesis in 1), 1 from left ventricular outflow obstruction (by a porcine bioprosthesis), 2 from technical mishaps (incision into left ventricular free wall with rupture in 1 and ligation of the left circumflex coronary artery with resulting acute myocardial infarction in 1) and 2 died suddenly for reasons not determined. Of the 6 patients dying greater than 60 days after operation, 4 died from chronic congestive cardiac failure, 1 from a cerebral embolus and 1 from prosthetic valve endocarditis.