Thirty-one elderly depressed patients were treated for seven weeks with nortriptyline with plasma levels kept between 50-180 ng/ml. Electrocardiograms were taken at the third and seventh weeks of treatment. There were significant increases in the PR interval, QTc interval, and heart rate from before and after treatment. However, there were no consistent correlations between electrocardiographic changes during treatment and plasma levels of nortriptyline, 10-hydroxynortriptyline and either of its two isomers (E-10-hydroxynortriptyline, Z-10-hydroxynortriptyline). Increased QRS duration after seven weeks of treatment was correlated with daily dose of nortriptyline.