OBJECTIVE: To determine the safety of Very low calorie diets (VLCD) in regard to their effects on cardiac function, DESIGN: EKG changes were analyzed for 126 women on a VLCD of 3349 kJ/d (800 kcal/d), EKGs were done when the diet was begun, after 3 months of dieting, and at a 6 month follow up after being off the diet for 3 months, SETTING: Subjects were solicited through advertisements and charged $1,000 for participating after being screened for age, weight, and health status. MAIN OUTCOME MEASURES: EKG QTc intervals, PR interval, QRS interval, ST-T wave changes, and heart rate. RESULTS: Over one-fourth (27.0%) of subjects had normal EKGs at all three time points studied, Sinus bradycardia was the most common abnormality, observed in 60 subjects (47.6%) on at least one of the three EKGs, Fifty-eight (46%) patients had EKGs with ST-T wave abnormalities observed on at least one of the EKGs, Eight subjects (6.4%) had prolonged QTc (more than one standard deviation beyond the average for women) intervals on at least one EKG, None of these eight persons had significant untoward medical consequences, CONCLUSION: A VLCD diet of 3349 kJ/d (800 kcal/d) for up to 3 months is not associated with significant electrocardiographic abnormalities or clinical cardiac complications, provided the patients have low cardiovascular risk at baseline.