<qa>  What is the ECT treatment of depressed patients that exhibits a therapeutic response toTo be determined is whether the exaggerated platelet reactivity and diminished HRV exhibited by depressed patients are affected by treatment with ECT. Autonomic function in depressed patients will be studied longitudinally before and after ECT. Heart rate variability HRV in depressed patients who exhibit a therapeutic response to ECT and who exhibited diminished HRV prior to treatment will support the hypothesis that HRV are pathophysiologically associated with the state of major depression. Successful ECT treatment of depressed mood that is not associated with normalization of HRV may indicate that: a HRV is unrelated to Major Depressive Disorder, or b HRV may reflect a pre-existing trait phenomena of major depressive disorder, or c directly improve HRV. 