Tho effects of native isosorbide mononitrate ( ISMN ) on the hemodynamics in rats with early myocardial infarction by left coronary artery occlusion were investigated. LVSP and dP/dtMAX were increased, and LVEDP was decreased with ISMN 5mg/kg i.v. 20 min after coronary occlusion. However, ISMN did not significantly effect the HR, SAP, DAP and MAP. The results showed that ISMN can improve cardial function in early myocardial infarction.