AbstractVentricular fibrillation during coronary angiography with Renografin‐76 has been attributed to the high osmolar ionic and calcium binding additive properties. Isovue‐370 is a new low osmolar nonionic contrast medium lacking calcium binding additives. The present investigation compared the incidence of contrast media‐induced ventricular fibrillation in patients undergoing coronary angiography with Renografin‐76 to that with Isovue‐370. Group I consisted of 2,000 consecutive patients undergoing coronary angiography with Renografin‐76, and group II consisted of 2,000 subsequent consecutive patients in whom lsovue‐370 was employed as the contrast medium. There was no significant difference between groups I and II with respect to volume of contrast media used per patient (125 ± 35 vs. 140 ± 45 ml), age (63.5 ± 15 vs. 60 ± 17 years), sex (74% male vs. 76% male), ejection fraction (55% vs. 55%), valvular heart disease (8% vs. 9%), prior coronary artery bypass graft surgery (5.8% vs. 5%), or extent of coronary artery disease. Contrast media‐induced ventricular fibrillation occurred in 20 patients in group I (incidence 1%), whereas eight episodes occurred in group II (incidence 0.4%) (P<0.03). Thus the present investigation suggests that the incidence of ventricular fibrillation during coronary angiography can be significantly decreased by using low osmolar nonionic contrast media lacking calciu