BACKGROUND: Use of radial artery (RA) for coronary artery bypass grafting (CABG) is an increasingly common practice. The objective of our study was to compare the effects of two drugs as antispastic agents in patients undergoing CABG. METHODS: Sixty patients, submitting to CABG using the RA, were randomly assigned to two treatment groups (n = 30 in each group). Following the induction of anesthesia, the two groups were administered either 0.2-2microgram/kg/min nitroglycerin or 0.05-0.1 mg/kg/hr diltiazem as a continuous IV infusion. CABG in both groups was performed as per standard surgical protocol. RESULTS: The peak serum creatinine phosphokinase-MB level (59.3 ng/ml for nitroglycerin treatment versus 57.7 ng/ml for diltiazem treatment), postoperative ejection fraction (52.3% versus 48.4%), duration of stay in the ICU and total length of hospital stay were not significantly different between the groups (P > 0.05). However, the need for inotropic agents to prevent or treat intraoperative hypotension was less for patients in the nitroglycerin group than for patients in the diltiazem group (60.0% to 83.3%). CONCLUSIONS: Our results indicate that nitroglycerin is superior to diltiazem as an antispastic agent. We suggest that nitroglycerin should be the agent for choice for the prevention of conduit RA spasm.