The isolated rat heart model was used to examine the effect of a new nonionic contrast agent, B-15,000 (Iopamidol), on cardiac function. Comparative studies were performed with Amipaque, Renografin 60, Renografin 76, and Vascoray. The three ionic contrast agents had significantly greater detrimental effects on cardiac function than either nonionic agent. The results support the continued evaluation of the nonionic agents for use in coronary angiography.