THE USE of fibrinolytic agents in the treatment of acute coronary thrombosis seems to offer promising results. Various reports have been made that fibrinolysins have been used intravenously with encouraging results for the lysis of thrombi at numerous sites within the vascular system.1,2,3Thrombi have been artificially produced in coronary arteries by various methods and, after their creation, treated with fibrinolytic agents.4However, these methods involved considerable dissection of the coronary arteries, with partial ligation of segments of the vessels, and the injection of the thrombus into an isolated segment of a coronary artery, with temporary proximal and distal occlusion of the selected site. Our objective was to place into the coronary arterial system a thrombus of the clotted blood of the animal operated on, and to do so without imposing trauma or other abnormal conditions on the coronary arteries. Accordingly, we believed that the