Electroconvulsive therapy (ECT) is used frequently in psychiatric practice and various electrocardiographic (ECG) changes have been described during ECT. QT dispersion (defined as maximal QT interval minus minimal QT interval) as assessed on the surface electrocardiogram has been demonstrated to reflect regional inhomogeneity of ventricular repolarization. The aim of this study is to examine the effect of electroconvulsive therapy on QT dispersion. We studied 27 patients (age range 24-42 y, mean age 34 y, 11 men) without heart disease who were treated with ECT. Structural heart disease was eliminated with routine clinical examination and laboratory tests, echocardiography, and exercise treadmill test. QT interval and corrected QT (QTc) dispersion was measured on a 12-lead ECG before and just after ECT. QTc dispersion increased from 28.9 +/- 7.4 ms at baseline to 81.4 +/- 12.8 ms after the procedure (P < 0.0001). This result demonstrated that QTc dispersion increased significantly during ECT. This finding may explain that increased inhomogeneity of ventricular repolarization is associated with enhanced vulnerability to arrhythmias during ECT.