In dogs with a 2-4 day old myocardial infarct and a predominantly sinus heart rhythm, we examine arrhythmogenic potencies of amrinone (0.5 mg/kg/min, 1 and 3 mg/kg) and milrinone (10 micrograms/kg/min, 75 and 100 micrograms/kg). 2. Amrinone and milrinone significantly reinduced ventricular ectopic beats on day 2 after coronary occlusion. 3. These effects were preceded by a cardioacceleration which intensified as the ventricular arrhythmias developed. 4. Over the following days the arrhythmogenic potencies of these inotropic drugs were modest. 5. Thus, amrinone and milrinone can impair heart rhythm chiefly in a recent myocardial infarct.
