We have done a double-blind randomized study to compare the cardiac effects of 2 nonionic low osmolality contrast agents, iohexol (n = 25) and iopamidol (n = 25), for left ventriculography and coronary arteriography. No statistical differences were detected between both groups in quality of image, clinical (absence of nausea; intense warmth [8% vs 8%, p = NS]) and electrocardiography (repolarization changes [24% vs 12%, p = NS], absence of severe bradycardia and ventricular arrhythmia) effects. Ventriculography induced no change in systolic left ventricular pressure (iohexol: 128.6 +/- 18 vs 127 +/- 19 mmHg, p = NS; iopamidol: 133 +/- 24 vs 131.8 +/- 23 mmHg, p = NS), and a little but significant rise in left ventricular end-diastolic pressure (iohexol: pre = 11.6 +/- 7 vs post = 13.9 +/- 7 mmHg, p less than 0.01; iopamidol: 11.7 +/- 4 vs post = 15.5 +/- 5 mmHg, p less than 0.001). Our results suggest that iohexol and iopamidol are comparable and qualified for angiocardiography.