The hemodynamic effects of trazodone (150 mg) and imipramine (75 mg) were examined in eight healthy subjects. Trazodone significantly increased left ventricular ejection time 1 (LVETI), but decreased both preejection period (PEP) and PEP/LVET ratio. It also decreased heart rate and systolic and diastolic blood pressure at 90 min after dosing. Imipramine initially increased total electromechanical systole I (QS2I) and PEP (30 min, P less than 0.01), but at 150 and 180 min after dosing QS2I was significantly lower. Imipramine increased diastolic blood pressure at 30 min (P less than 0.05) and increased systolic blood pressure between 90 and 180 min (P less than 0.05). At 30 and 60 min heart rate was significantly depressed by imipramine. There were no significant changes in the values of stroke volume and cardiac output. These results suggest that trazodone has its major effect on the circulation through its alpha-receptor blocking activity, whereas the effects of imipramine are probably mediated through its ability to block reuptake of norepinephrine.