This chapter discusses potential mechanisms of antidepressant action and outlines areas of active research in electroconvulsive therapy. Electroconvulsive treatment (ECT) remains the most effective treatment for major depression. During the seizure itself, and for a period of hours afterward, there is higher sympathetic tone with markedly elevated heart rate and blood pressure during ictus and for several minutes postictally. Pre-existing seizure disorder is generally not a contraindication for ECT; however, in patients with seizures, it should be ascertained that the seizure is not caused by a mass lesion or vascular malformation which could constitute higher risk with ECT. ECT requires the consent of the patient or, in the event that the patient lacks capacity, a ruling from a legal authority regarding procedures for substituted consent if available. The most common adverse effects of ECT are headache and myalgia.