Cardiac function and left ventricular dynamics were measured in seven consecutive patients 1 day before and 6 months after percutaneous transluminal balloon angioplasty of subtotal proximal stenosis of the left anterior descending coronary artery. Before angioplasty all patients had obvious left ventricular dysfunction during exercise and to a smaller degree during isoproterenol infusion; the condition of all patients was greatly improved 6 months after angioplasty. After angioplasty, left ventricular end-diastolic pressure was normal at rest and decreased from a mean (+/- standard error of the mean) of 33.8 +/- 1.6 to 19.2 +/- 0.5 mm Hg on exercise. Left ventricular ejection fraction, measured by a gated blood pooling technique with technetium-99m, improved on exercise from 46 +/- 5.0 percent to 69 +/- 1.0 percent. Cardiac output and stroke volume index increased significantly with exercise after angioplasty. The peak negative rate of pressure reduction in the left ventricle (dP/dt/min), an index of left ventricular relaxation, was highly abnormal on exercise before (2,307 +/- 260 mm Hg/s) and increased to the normal range (3,154 +/- 200 mm Hg/s) after angioplasty. The improvement in left ventricular function after transluminal angioplasty in these cases of proximal left anterior descending coronary arterial stenosis is extremely encouraging.