In 9 patients with coronary heart disease isovolumetric contractility indices and ejection phase parameters were measured simultaneously, using an angiographic catheter with a manometer at the tip (Millar). Regional wall motion at rest, after leg raising and during physical exercise (bicycle ergometer) was analyzed applying the hemiaxis method. Five weeks after aortocoronary bypass surgery the same examinations were repeated. Preoperatively left ventricular enddiastolic pressure (LVEDP) increased from 21 to 37 mm Hg following leg raising. The velocity mean of fiber shortening (Vcf) and of regional fiber shortening in the anterior wall decreased significantly.--All patients discontinued physical exercise due to angina pectoris. LVEDP increased from 21 to 39 mm Hg. Large hypokinetic and akinetic areas developed especially in the anterior wall. Velocity of fiber shortening of the anterior wall decreased from 1.43 to 0.76/s. Enddiastolic volume remained unchanged while endsystolic volume increased significantly. In six patients with patent grafts surgery had a beneficial effect. Comparing angiograms at rest no significant changes were found. After leg raising and physical exercise, however, marked improvement in ventricular function occurred, compared to the preoperative performance. All 6 patients were exercised without complaints at a load of 100 watts for 8 minutes. Velocity of fiber shortening in the anterior wall increased significantly from 0.76 to 2.56/s, mean Vcf from 1.11 to 2.12 circ/s, max dP/dt from 2302 to 4280 mm Hg/s and Vpm from 27.8 to 55.7/s. Functional improvement in individual wall segments amounted to 500% in the mean. Ejection fraction increased from 54 to 76%. Enddiastolic volume remained unchanged while endsystolic volume decreased from 67 to 33 ml/1.37 m2 (p less than 0.002). In three patients the bypass occluded or myocardial infarction occurred intraoperatively. Postoperative findings at rest and during exercise were unchanged as compared to preoperative values. Following successful bypass surgery ventricular function at rest did not change. During exercise, however, a marked improvement in overall and in regional ventricular function was found.