Previous studies have indicated that nicorandil reduces both preload and afterload, clearly distinguishing nicorandil from conventional nitrates, whose predominant action is that of preload reduction. In association with the decrease in afterload following nicorandil, the contractile responses during isovolumic contraction and relaxation improved significantly, indicating that nicorandil does not demonstrate negative inotropic actions. Furthermore, despite a marked decrease in mean aortic pressure after nicorandil, coronary sinus blood flow remains unchanged. Therefore, coronary vasodilatation must have taken place, while myocardial oxygen consumption decreased significantly. The vasodilatory action of nicorandil on the epicardial coronary artery has also been demonstrated in our previous study. Nicorandil, at a dose of either 20 or 40 mg, induces a significant increase in coronary artery diameter favourably by acting not only on the non-stenotic but also on the stenotic coronary segments. In our recent study, the effects of intracoronary nicorandil (6 mu.kg-1) and isosorbide dinitrate (2 mg) on the epicardial coronary arteries were investigated in patients undergoing coronary angioplasty. In non-stenotic coronary artery segments, the mean coronary diameter increased significantly after either nicorandil (+12%) or isosorbide dinitrate (+17%). In stenotic segments, however, increase in the diameter of the obstructed segment by 20% after intracoronary nicorandil was much more pronounced when compared to that of 8% after isosorbide dinitrate. There was a significant additional increase of 13% in the diameter of the obstructed segment when nicorandil was administered following isosorbide dinitrate, while no such additional effect was observed when isosorbide dinitrate was given after nicorandil.(ABSTRACT TRUNCATED AT 250 WORDS)