PURPOSE: We'd like to know the relationship between the changes of cardiac function and systemic O2 consumption according to the increasing dose of dopamine. METHODS: Ten rabbits(from 2kg to 2.8kg) were used in this experiment. Anesthesia was induced with intraperitoneal pentobarbital sodium(35mg/kg) and tracheostomy was done. It was maintained by ventilation with a mixture of 1-3% halothane and 67-69% oxygen. Polyvinyl catheters were inserted into the femoral artery and vein and to check blood pressure and arterial blood gas analysis during the surgical procedure. Two other catheters were inserted into the internal carotid artery and external jugular vein and advanced into left ventricle and right atrium to check the pressure of each chamber, LV maximal dP/dt and to obtain blood samples of each chamber. Thoracotomy was done to expose aorta and coronary artery to check the cardiac output and coronary blood flow. We injected dopamine every 10 minutes according to the scheduled dose through external jugular vein and recorded heart rate, cardiac output, aortic pressure, maximal dP/dt, coronary blood flow by computer. Systemic O2 consumption was calculated by Fick method RESULTS: The heart rate and mean aortic pressure increased slowly according to the dose of dopamine from 20 microgram/kg/min. The cardiac otuput the maximal dP/dt and coronary blood flow was not changed until 5 microgram/kg/min, but from 7.5microgram/kg/min, it increased according to the dose of dopamine. CONCLUSION: Dopamine was a powerful inotrophic agent without increasing the systemic O2 consumption until 20microgram/kg/min, but systemic O2 consumption increased markedly at more than 20 microgram/kg/min of dopamine.