Increased dispersion of ventricular recovery time is believed to be a substrate for serious ventricular arrhythmias. Class III antiarrhythmic drugs probably operate by decreasing dispersion through homogeneous prolongation of recovery time. A single surface QT value gives no information on recovery time dispersion but interlead variation in QT may be relevant. QTc dispersion was measured in 67 patients post myocardial infarction randomized to treatment with either sotalol or placebo. QTc dispersion was calculated as the difference between the maximum and minimum QTc in any surface electrocardiogram lead. Both maximum QTc and QTc dispersion varied considerably following infarction but throughout the 6-month follow-up period maximum QTc was significantly greater (P less than 0.05) and QTc dispersion significantly less (P less than 0.05) in patients on sotalol compared with placebo. These findings are in accord with expected changes in ventricular recovery time and provide strong support for the hypothesis that surface electrocardiogram QT variation reflects regional differences in ventricular recovery time.