The purpose of this study was to determine the role of coronary collaterals on global left ventricular function during transient coronary occlusion. Left ventricular systolic function was evaluated noninvasively in 37 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) by means of peak aortic blood acceleration measured with a continuous-wave Doppler velocity meter placed suprasternally. Doppler measurements were made before, during, and immediately after balloon inflation. Nineteen patients underwent PTCA of the left anterior descending coronary artery, 15 of the right coronary artery, and three of the circumflex coronary artery. All patients had a subtotal coronary occlusion. Among the 37 patients 23 had no angiographic evidence of collaterals supplying the vessel undergoing PTCA and 14 had collaterals. In patients without collaterals peak acceleration was 16.0 +/- 3.0 m/sec/sec before balloon occlusion and decreased to 11.8 /+- 3.6 m/sec/sec within 30 to 40 seconds of coronary occlusion (p less than 0.001). After 30 to 40 seconds of reperfusion (balloon deflated), peak acceleration returned to near- preocclusion levels (17.3 +/- 7.5 m/sec/sec). Among patients with collaterals peak acceleration remained unchanged during balloon occlusion and reperfusion relative to preocclusion levels (NS). These data indicate that collaterals can preserve left ventricular function during transient coronary occlusion in humans.