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The advantage of producing myocardial infarction by selective injection of emboli into the coronary circulation has been previously emphasized( 1 ) . In the present study myocardial infarction was produced by injecting relatively large ( 1 . 1 mm in diameter) steel ball bearings into the circumflex branch of the left coronary artery. The ball bearings are large enough to remain in the coronary system and to be easily seen by fluoroscopy and radiography. Coronary arteriograms were obtained before and after embolization, to determine the extent of the coronary vascular system occluded by the emboli and to attempt to demonstrate changes in the caliber of the coronary arteries,The changes in hemodynamics and myocardial metabolism occurring as a result of the myocardial infarction produced are reported here.Material and methods. Twenty-three experiments were carried out. Large mongrel dogs weighing 1 8 kg or more were used. Anesthesia was produced by Pentobarbital ( 2 5 mgJkg of body weight) given intravenously. ICatheters were introduced through the left carotid artery, external jugular vein, and right brachial vein and artery. Pressures were obtained from the right and left atrium and ventricle, ascending aorta and pulmonary artery. Statham strain gauges and a Sanborn Polybeam recorder were used for registering the pressures. A dye dilution curve was recorded by injecting 5 mg of indocyanine green into the right atrium with continuous sampling from the aorta through a Gilford densitometer ( 2 ) . The cardiac output was calculated by the Hamilton method(3). The coronary sinus was then intubated and simultaneous arterial and coronary venous blood was drawn for determination of coronary blood flow (4), oxygen ( 5 ) , glucose ( 6 ) , lac-* This investigation was supported by U.S.P.H.S.grant HTS 5482 C2. tate ( 7 ) , pyruvate (8), and free fatty acids ( 9 ) . The circumflex branch of the left coronary artery was then catheterized with a No. 7 aortographic catheter, under fluoroscopic control. A coronary arteriogram was obtained by injecting 2 cc of sodium iothalamate (Angioconray) and utilizing the spot film device of the Picker image amplifier. Steel ball bearings ( 1 . 1 mm in diameter) were then injected into the intubated coronary artery.In 12 experiments, 2 to 3 ball bearings/kg of weight were injected, in the remaining, 4-5 ball bearings/kg of weight. Three cubic centimeters of normal saline solution was used to carry the ball bearings through the catheter. Further flushing of the catheter, when needed, was done by repeatedly drawing and reinjecting blood from the cannulated coronary artery. A second coronary arteriogram was obtained from 1 to 5 minutes following the embolization. The catheter was then withdrawn into the aorta. In 4 experiments the second coronary arteriogram was obtained at the end of the procedure. After 4 5 minutes to 1 hour, all basal determinations were repeated. The blood volume was maintained constant in all experiments where blood was drawn. Metabolic studies were done in only the first 1 0...