Are ioxaglate and iopamidol equally safe and well tolerated in cardiac angiography? A randomized, double-blind clinical study. A randomized, double-blind, parallel-group study was performed in 50 patients undergoing left ventriculography and coronary arteriography to evaluate ECG changes and the effects on left ventricular function of a low-osmolar ionic contrast agent, ioxaglate, as compared with a low-osmolar nonionic contrast medium, iopamidol. Twenty-five patients received ioxaglate (group 1) and 25 patients received iopamidol (group 2). All patients underwent 48 hours of continuous ECG recording beginning 24 hours before the cardiac catheterization. Left ventricular systolic and end-diastolic pressure, peak positive dp/dt, and dp/dt/P ratio were measured immediately before and after left ventriculography and 3 minutes later. Left ventricular systolic pressure did not change after injection of either contrast medium. Left ventricular end-diastolic pressure increased by 30% in group 1 (p less than 0.01) and by 22% in group 2 (p less than 0.01) immediately after left ventriculography. A further increase by 45% in group 1 (p less than 0.01) and by 24% in group 2 (p less than 0.01) was observed 3 minutes later. No differences were observed between values obtained in the two groups. Peak positive dp/dt did not change immediately after injection of either contrast medium but decreased by 5% (not significant) in group 1 and by 7% (p less than 0.02) in group 2 three minutes after left ventriculography. There were no significant differences between the two groups. Analysis of continuous 48-hour ECGs showed that both ioxaglate and iopamidol induced a slight increase (by 8% and 7%, respectively; p less than 0.05) in heart rate during injection with early and complete recovery. 