Previous studies of left ventricular performance (LVP) in depressed patients receiving tricyclic antidepressants have been performed on patients without severe heart disease. This study reports the effect of imipramine hydrochloride on LVP, assessed by radionuclide angiography, in a group of depressed patients with notable preexisting left ventricular dysfunction. Ejection fraction was measured at rest by first-pass radionuclide angiography before and after treatment with imipramine. Ejection fraction was unchanged during treatment, but seven of 15 patients experienced orthostatic hypotension of such severity that administration of the drug had to be discontinued. Plasma concentrations of the drug were essentially twice those usually seen. It is important to appreciate that although imipramine does not further impair resting LVP, this does not mean it is without risk. The physician must watch carefully for orthostatic hypotension when using imipramine in depressed patients with impaired LVP.