Increased QT dispersion (QTd) is a noninvasive marker of an electrophysiologic abnormality associated with high mortality in coronary artery disease. The purposes of this study were to measure changes in QTd and ST-segment changes immediately before, during and after intracoronary balloon inflation and to determine whether the coronary artery vessel involved and/or the duration of inflation affect(s) QTd. A total of 45 patients (32 men, 13 women, mean age 58 +/- 11 years) who were referred for elective percutaneous transluminal coronary angioplasty were included. The mean QT interval dispersions for all patients before the inflation, during the balloon inflation at 60 sec and after the balloon deflation at 5 min were 68 +/- 13 ms, 82 +/- 16 ms and 71 +/- 13 ms, respectively. There was no significant difference between baseline and 5 min after deflation. The increase in QTd during the balloon inflation was significant (p<0.01). There was no significant QTd change in patients with left circumflex artery (Cx) lesions during inflation and after deflation compared with baseline. The differences were statistically significant only in patients with left anterior descending (LAD) lesions and right coronary artery (RCA) lesions at 60 sec during balloon inflation (p=0.001 vs. p=0.04). Acute reversible myocardial ischemia induced by balloon inflation causes an increase in QTd limited to the LAD and RCA vessels. Therefore, when using QTd as a marker of myocardial repolarization abnormality due to acute reversible ischemia, the involved coronary artery vessel must be taken into account.