Beta hydroxytrimethylammonium butyrate[L-carnitine] is highly concentrated in myocardium and it is essential substance for transfer of fatty acids into the mitochondria. We respect that L-carnitine has protective action to myocardium during ischemia. I studied coronary flow and CK - MB isoenzyme of coronary effluent of Langendorff`s isolated rat heart model. As a control group 5 Sprague-Dowley species rat hearts were connected to Langendorff`s isolated rat heart model and perfused for 30 minutes with Kreb-Henseleit buffer solution. After cessation of perfusion for 30 minutes they were reperfused for 30 minutes. In experimental group 10 Sprague-Dowley species rat hearts were perfused with 10mmole /L of L-carnitine contained in Kleb-Henseleit buffer solution. In equilibrium state, coronary flow was 1.7 times greater in experimental group. During reperfusion, both group showed equally decreased flow amount of about 60% of that of equilibrium state. CK-MB isoenzyme level of perfused coronary fluid showed no significant difference in equilibrium state. In reperfusion. CK-MB isoenzyme levels of control group were 17.61$pm$8. 68U/L at 25 minutes, 23.32$pm$4.15U /L at 30 minutes; and in experimental group, 13.63$pm$6. 08U/L at 15 minutes and 13.6$pm$8.41U /L at 30 minutes respectively. Those values in both states showed significantly lower CK-MB level in experimental group. In conclusion, L-carnitine prevent ischemic myocardial damage during ischemic and reperfusion state of Langendorff`s isolated rat hearts and also I suggest the L-carnitine act potent coronary vasodilator during preischemic and postischemic states of rat hearts.