This study was undertaken to examine the effects of mianserin (MIA), a tetracyclic antidepressant, and adinazolam (ADI), a new benzodiazepine antidepressant on cardiac function and electrocardiogram in normal and infarcted hearts of anesthetized dogs, and to compare the effects with those of amitriptyline, a commonly used tricyclic antidepressant. The parameters measured were: heart rate (HR); mean arterial blood pressure (MP); aortic flow (AF); maximal rate of increase of left ventricular pressure (LV dp/dt); blood flow of left circumflex of left coronary artery (CAF) and PQ and QRS intervals. The double product (DP) was calculated from HR and the arterial pressure. AMI increased HR, DP, LV dp/dt and CAF in the normal group, while in the infarcted group, AMI increased HR, DP and CAF, but decreased LV dp/dt at 3 mg/kg. AMI at 2 and 3 mg/kg prolonged QRS intervals in the infarcted groups. MIA increased HR and DP in the normal group at doses of 1 mg/kg or more, while in the infarcted group it produced only slight effects in hemodynamic parameters and PQ and QRS intervals. ADI had little effect on hemodynamics and PQ and QRS intervals in the normal group. However, it decreased LV dp/dt, CAF, MP at 3 mg/kg in the infarcted group. In conclusion, AMI markedly influenced cardiac hemodynamics and QRS interval in the myocardial infarcted group, while, on the other hand, MIA and ADI, in clinical doses, had only a slight effect on hemodynamics and PQ and QRS intervals in the infarcted group. Thus MIA and ADI were safer than AMI in the animals with myocardial infarction.