A multicentered double-blind randomized study was performed comparing the electrocardiographic and hemodynamic changes induced by two new low osmolar contrast agents used for cardiac angiography. The low osmolar ionic (ioxaglate) contrast agent was compared with a low osmolar nonionic (iopamidol) contrast agent in 150 patients with angina pectoris undergoing angiography. Systolic blood pressure, left ventricular end-diastolic pressure, heart rate, and QT interval were measured just before and for 90 s following the left ventricular angiography and selective coronary angiography. Each group was also evaluated for adverse events and quality of radiographic images. Following left ventricular angiography, the systolic blood pressure dropped slightly in both groups with a greater decrease seen in the iopamidol group at 5 s (p less than 0.05). After selective right and left coronary angiography, systolic blood pressure decreased transiently and equally in both treatment groups. The left ventricular end-diastolic pressure increased after the ventriculogram in both groups (15.9 +/- 6.3 to 18.9 +/- 8.6 mmHg in the ioxaglate group and 16.1 +/- 6.7 to 20.1 +/- 7.8 mmHg in the iopamidol group), the change being significant only in the iopamidol group (p less than 0.05). Heart rate increased slightly but significantly in the ioxaglate-treated patients following left ventricular angiography (71.4 +/- 15.2 to 74.4 +/- 13.7 beats/min) (p less than 0.01). QT interval transiently increased following left ventriculography with ioxaglate (407 +/- 59.5 to 420 +/- 58.3 ms) (p less than 0.05) compared with iopamidol.(ABSTRACT TRUNCATED AT 250 WORDS)