Nicorandil, a hybrid nitrate and ATP-sensitive potassium channel opener, has had a preconditioning effect in some coronary angioplasty studies. The present study investigated whether the cardioprotective effects of nicorandil involve coronary collateral function. Thirty-two patients with stable angina pectoris were randomized to receive a 1-min intravenous infusion of nicorandil (100 μg/kg) or normal saline. Five minutes later they underwent three 2-min balloon inflations 5-min apart. The maximum ST-segment elevation (ΔSTmax), the sum of ST-segment elevations in all leads (ΣST), and the chest pain score were determined at the end of each balloon inflation. The collateral flow index (CFI) was derived from simultaneous measurement of the mean aortic pressure and the coronary wedge pressure obtained from a pressure guidewire during balloon inflation. The ΔSTmax, ΣST, and chest pain score decreased progressively during the 3 sequential balloon inflations in both groups, and the ΔSTmax and ΣST were less in the nicorandil group than in the control group during each inflation. The CFI did not change during the 3 inflations in either group and was similar in the 2 groups during each inflation. In conclusion, pretreatment with intravenous nicorandil enhances myocardial tolerance to ischemia without progressive collateral recruitment during coronary angioplasty. (Circ J 2002; 66: 317 - 322)