Increased QT dispersion predicts the occurrence of lethal ventricular arrhythmias complicating percutaneous transluminal coronary angioplasty (PTCA). Moreover, these arrhythmias occur more frequently at the first balloon inflation. Activation of the K(ATP) channel may influence QT dispersion and ventricular arrhythmias during coronary angioplasty, so 40 consecutive patients with stable angina were randomized to receive 3 mg/h of nicorandil infusion or placebo and QT dispersion and the incidence of ventricular ectopy were investigated before and throughout PTCA. There were no significant differences in QT dispersion at baseline between the nicorandil group (42+/-8 ms) and placebo (42+/-12ms). At the first balloon inflation, the QT dispersion in the nicorandil group (51+/-13 ms) was significantly less than that observed with placebo (76+/-16ms, p<0.001). However, the QT dispersion at the second inflation was similar in both groups (nicorandil: 45+/-12ms; placebo: 52+/-14ms). Ventricular ectopy was observed in 1 patient receiving nicorandil and 5 patients in the placebo group during the first inflation, and none in the nicorandil and 1 patient in the placebo group during the second balloon inflation. Activation of the K(ATP) channel may inhibit the development of ventricular arrhythmias during PTCA, particularly at the first balloon inflation.