Quazodine (also known as MJ-1988) is a quinazoline derivative patented by Fujisawa Pharmaceutical Co. as a muscle relaxant. In cats anesthetized with sodium pentobarbitone. Quazodine decreased diastolic blood pressure, peripheral vascular resistance, systolic ejection time and left ventricular end-diastolic pressure in cats. Heart rate, cardiac effort, output, and external work and left ventricular dP/dt were markedly increased. In the intact dog, as well as in the heart-lung preparation., the stimulant action on the force of myocardial contraction was accompanied by increases in coronary blood flow, pulmonary vasodilation, and bronchodilation. Administration of larger doses caused depression of cardiac function and initiated cardiac arrhythmias.