Experiments on open-chest anaesthetized cats were made to test derivatives of crown ethers, such as benzylase-15-crown-5 and dibenzylase-15-crown-5 for their effects on myocardial ischemia and the functional status of a myocardial ischemic focus in temporary coronary occlusion during coronary spasm induced by dihydroergotamine and during coronary microthrombosis caused by ADP. When intravenously administered in doses of 0.5-15 mg/kg, the tested agents were found to enhance myocardial tolerance to ischemia, depressed ST segment in ischemia induced by coronary occlusion and administration of ATP, and prevented ST-segment depression during coronary spasm.