The function of the left ventricle is important for the success of surgery. To differentiate between normal and abnormal ventricular function, the contractile and relaxation reserve was measured. In 19 patients, 10 with mitral and 9 with aortic valve disease, max dP/dt and min dP/dt were measured at rest and during exercise (ergometer). Max dP/dt increased in 7 patients above 3200 mm Hg/s and dP/dt/P above 60 s-1 (normal contractile reserve). Only 3 of these patients reached a normal increment of relaxation velocity (min dP/dt above 2400 mm Hg/s). In 12 patients the contractile and relaxation reserve was decreased. All patients with mitral stenosis had abnormal relaxation reserve despite normal contractile function in 4 cases. Left ventricular enddiastolic pressure did not correlate well with myocardial dysfunction. Isovolumic contractility during exercise was decreased in patients with aortic valve disease. Enddiastolic pressure increased from 18 +- 8 to 22 +- 14 mm Hg during exercise.