The change of venous capacitance has an influence on venous return to the heart and cardiac output, and causes the alteration of preload, cardiac filling pressure and myocardial wall tension. Venous capacitance is assesed by measuring the mean circulatory filling pressure (MCFP), and MCFP is measured during brief periods of circulatory arrest produced by inflating an indwelling balloon in the right atrium It is important to know the effects of vasodilator and anesthetic drugs on venous capacitance. Therefore, this study was performed to know the effects of nitroglycerin and diltiazem on venous capacitance in rats. Rats were anesthetized with ketamine 125 mg/kg given intraperitoneally and added 10 mg/kg every 30 minutes. Their mean arterial pressure (MAP) was lowered to 60 mmHg by intravenous injection of 0.82±0.36 mg/kg nitroglycerin and/or 6.7±1.5 mg/kg diltiazem. Hemodynamic parameters such as MAP, heart rate, central venous pressure and MCFP were measured before and after drug-injection. Hemodynamic values measured before drug-injection in two groups were little differences statistically. However, the MCFP of nitroglycerin was significantly decreased (p<0.01) from 7.3±0.61 mmHg to 5.4±0.58 mmHg after drug-injection, and that of diltiazem was not significantly changed from 7.1±0.54 mmHg to 6.9±0.63 mmHg. The results suggested that nitroglycerin was predominantly a venous dilator in terms of MCFP but diltiazem had little effect of venodilation.