Ten patients with severe effort angina and with left ventricular dysfunction during exercise before operation underwent haemodynamic and angiographic studies in average 20 months after coronary artery bypass surgery. Five patients (50%) were completely asymptomatic after operation(group I). The other five (group II) were still limited physically because of anginal pain, although two were much improved. Pre-operatively there was no significant difference in the severity of the disease, as judged from case histories, work tests and haemodynamic and angiographic findings between the two groups. The working capacity of the patients in group II was not increased significantly post-operatively. Their coronary arteriograms revealed unsatisfactory surgical results. In two patients, one significantly stenosed vessel was not bypassed because of poor run-off. In the other three patients, one graft was closed. Left ventricular function curves showed no significant improvement of left ventricular pump function. In group I, working capacity increased significantly, all stenoses of major coronary vessels were bypassed and all grafts were patent. Left ventricular function showed an almost normal response during exercise. These findings suggest that left ventricular dysfunction due to ischaemia can be significantly improved by coronary bypass and that there is a good correlation between clinical, haemodynamic and angiographic findings.