Few studies have examined the cardiovascular response to pulse unilateral electroconvulsive therapy (ECT) performed using modern techniques. In this study of 30 patients (mean age 62 years) with major depression, we determined the effects of pulse unilateral ECT on cardiac work load using the rate-pressure product (RPP), a product of pulse and systolic blood pressure. The mean RPP across all ECT treatments increased by an average of 96% from pre-ECT baseline, with the maximal RPP occurring typically during the seizure. The amount of increase in RPP did not differ significantly over the course of treatments. The increase in RPP was significantly and inversely related to baseline RPP, such that subjects with the highest baseline RPPs actually had smaller increases in RPP during the ECT treatments. The mean percent change in RPP was not associated with age, sex, presence of cardiovascular disease, ECT stimulus charge, EEG seizure duration, or amnestic side effects. There was a trend (p = 0.06), however, for the mean increase in RPP to be greater in responders (100% increase, n = 25) than in nonresponders (76% increase, n = 5). The potential relationship of clinical outcome to the increase in RPP suggests that both factors may be manifestations of the physiological intensity of the ECT-induced seizure.