Abstract: Objective To investigate effects of midazolam, etomidate, propofol and thiopental on contractility and coronary flow of isolated rat hearts. Methods Heart rate, left ventricular systolic pressure (LVSP), (LV+ dp/dtmax), (LV- dp/dtmax) and coronary flow (CF) were assessed in isolated rat hearts perfused with KHB solution containing different concentrations of midazolam, etomidate,propofol and thiopental. Results With increase of concentration, each agent caused progressive but differential decrease in LVSP, LV+ dp/dtmax, LV- dp/dtmax. At equal effective concentration, the rank order of inhibitory potency was thiopental ＞ propofol ＞ midazolam ＞ etomidate. High concentration of propofol and thiopental decreased heart rats. CF was increased by propofol at the concentration greater than 25 μmol/L, but was decreased by thiopental. No changes in CF were induced by midazolam or etomidate. Conclusion The results suggest that midazolarn, etomidate,propofol and thiopental decreased heart contractility in dose-dependent manner. The negative inotropic effect of propofol and thiopental is greater than that of midazolam and etomidate. Propofol, at clinically relevant concentrations, may affect autoregulation by causing coronary vasodilation.