Twenty obese women were randomly assigned to consume (for 16 wk) either a 420-kcal/d liquid diet (n = 12) or a 1200-kcal/d balanced diet (n = 8). Thereafter, patients in both conditions were prescribed a 1200-kcal/d diet for the remainder of treatment (week 45). Six obese nondieters served as control subjects. Ambulatory electrocardiographic (Holter) monitor readings were obtained on all patients at baseline and weeks 3, 9, 13, 17, 19, and 45 of the study and were analyzed for ventricular premature depolarizations (VPDs) per hour, paired forms, and runs of ventricular tachycardia. There were no statistically significant changes in VPDs in any condition during treatment. Similarly, there were no significant changes in the PR, QRS, and corrected QT intervals. The results indicate that under appropriate medical supervision, very-low-calorie diets can be used safely for up to 16 wk by significantly obese patients free of pre-existing cardiac disease.