In a total of 57 dogs the anterior descending branch of the left coronary artery was doubly ligated. Cortisone apparently (1) reduced the area of residual fibrosis; (2) All animals were sacrificed 14 to 22 days after operation.In group II (18 animals), the anterior descending branch of the left coronary artery was ligated 0.5 cm. below the origin of the circumflex branch (high ligation). Nine animals were treated with cortisone, 20 mg. twice a day for 20 days, and nine animals were kept as controls. All of these animals were sacrificed 30 days after operation. They had been confined to their cages until the time of sacrifice and had received 1 cc. of procaine penicillin (300,000 units) daily postoperatively for four days. Cortisone used in these experiments was given intramuscularly and the initial dose was given immediately as the coronary artery was ligated. Electrocardiograms (standard limb leads, augmented unipolar leads and V leads) were taken before, during and after ligation of the coronary artery. Upon sacrifice of the animals the heart and lungs were exposed and photographed in situ. Then the heart and lungs were removed en bloc. The hearts were studied by means of x-ray films of the injected coronary bed by the following technic: The right and left coronary arteries were isolated and a cannula was introduced into these vessels and tied. A 20 per cent suspension of bismuth oxychloride with a 20 per cent gum acacia base was injected through the cannula under pressure varying from 80 to 120 mm. Hg.2 X-ray films were then taken of the heart ( fig. 1).After injection, the hearts of all coronary ligated animals were fixed in 10 per cent formaldehyde for three days and then sectioned serially. The

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