BACKGROUND AND OBJECTIVES: A spasm of the radial artery is one of the most common complications of coronary angiography (CAG) via the transradial approach (TR), and this spasm sometimes disturbs the procedure. Nicorandil has recently shown dose-dependent dilatation of the blood vessels and ischemic preconditioning. This study was designed to evaluate the clinical effects and radial artery vasodilation of high dose nicorandil solution during CAG via the radial artery. SUBJECTS AND METHODS: This study was a prospective, randomized study to compare the effects of 12 mg of nicorandil (the Nicorandil group) and 10 mL of a cocktail solution (nitroglycerine 200 microgram mixed with verapamil 100 microgram) (the Cocktail group) in 146 patients. Vasospasms, which were expressed as the stenosis of the radial artery were examined at 2 parts of the radial artery. RESULTS: There were no significant difference of gender, age and risk factors for the 2 groups of patients. The reductions in the systolic and diastolic blood pressure (BP) 1 minute after drug administration were 33.6+/-11.4/10.4+/-7.7 mmHg in the Nicorandil group and 12.8+/-9.8/3.8+/-5.3 mmHg in the Cocktail group (p<0.001). Both vasodilating agents showed significant radial artery vasodilation after administration of the drugs (p<0.005 for all). The minimal luminal diameter (MLD) after drug administration was more dilated in the Nicorandil group than that in the Cocktail group (0.63+/-0.25 mm vs. 0.48+/-0.19 mm, respectively, p=0.013). CONCLUSION: Nicorandil solution was more effective for inducing vasodilation of the radial artery, but it was not clinical superior to the cocktail solution.