Background : Propofol(2,6-diisopropyl phenol) is an intravenous anesthetic agent, which was first introduced in 1986. It has 178.27 molecular weight and 1.8 fold stronger action of induction than that of thiopental. The effect of propofol, lowering blood pressure by depressing the cardiovascular system, has been mentioned in many papers, but its effect on myocardium is still in controversy and differs according to the method and interpretation of experiments used. This animal experiment was conducted to compare the effects of propofol and thiopental on myocardial contractility and coronary flow in isolated stunned rat hearts. Method : The hearts were isolated from twenty-four Sprague-Dawley rats and were perfused with modified Krebs solution. After isolation, the hearts were left in stabilizing period for 30 minutes. Then, myocardial stunning was induced by global ischemia for 15 minutes. In Group I, propofol was added to modified Krebs solution, which was used to perfuse the hearts at 40, 80, 120, 160, and 200 M concentration. In Group II, thiopental was added to perfusate at same concentration. Between each perfusion with anesthetic-added solution, the hearts in both groups were perfused with normal Krebs solution for 30 minutes to eliminate cumulative effect of anesthetics added. Left ventricular pressure, rate of ventricular pressure generation(dP/dt), and coronary flow were measured. Result : In both groups, anesthetics reduced left ventricular pressure and dP/dt in a dose dependent fashion. These changes were not statistically significant between two groups. However, at the 40 and 80 M concentration, the increment of coronary flow by propofol was significantly larger than that by thiopental. At the 120, 160, and 200 M concentration of propofol, coronary flow was gradually decreased with increasing concentration, and these decrease in coronary flow were not statistically significant between two groups. Conclusion : The effects of propofol on myocardial function were similar to those of thiopental in isolated stunned rat hearts and the increment of coronary flow might develop the coronary steal phenomenon. So, propofol may not have the benefit compare to thiopental for cardiac function. (Korean J Anesthesiol 1998; 35: 204∼214)