Cardiovascular effects of the tetracyclic antidepressant drug mianserin were examined in a prospective study including ten elderly depressed patients (age 60-77 years). During 1 week on placebo and 5 weeks on mianserin, 60 mg per day, orthostatic blood pressure testing, recording of standard electrocardiogram, 24-h electrocardiographic recording and systolic time intervals were carried out along with frequent monitoring of plasma levels of mianserin (13-57 micrograms/l) and the primary metabolite desmethylmianserin (7-27 micrograms/l). Mianserin caused a significant increase in orthostatic systolic blood pressure drop, and this correlated well with the plasma mianserin levels (rs = 0.70). There were no significant changes in supine blood pressure or in orthostatic changes in heart rate. No cardiac conduction disturbances or arrhythmias were provoked, but mianserin caused changes in systolic time intervals indicating impairment of left ventricular contractility and performance. Like tricyclic antidepressants mianserin should thus be used with caution in patients with latent or overt cardiovascular disease.