Combined mitral and aortic valve replacement with the Björk-Shiley tilting disc valve (pyrolite) was performed in 25 unselected patients characterized by markedly impaired functional capacity, hypokinetic central circulation and cardiomegaly before operation. Surgery was performed during extracorporeal circulation with deep hypothermia. The mitral valve was replaced first in all cases. There were no intra-operative deaths, but 2 patients died while still in hospital (8.0%). One patient died 2 months postoperatively due to progressive heart failure. The remaining patients--with the exception of one who had died of cancer of the ovary--were re-examined in average 28.7 (18-40) months postoperatively. Most patients had improved symptomatically and were in functional classes I-II (N.Y.H.A.). The haemodynamic findings indicated restoration to normal resting values of cardiac output, pulmonary artery pressure and pulmonary vascular resistance, but with an increase in left ventricular end-diastolic pressure (LVEDP). The mean diastolic gradient across the mitral prosthesis varied from 0 to 11 mmHg, while simultaneous pressure recordings from the left ventricle and the aorta, with one exception, disclosed no systolic pressure gradients (peak) across the aortic valve. Postoperative arterial thrombo-embolic complications occurred in 2 patients, resulting in only minor neurological sequelae.