OBJECTIVE The myocardial damage during ischemia and reperfusion in the rabbit was studied, in order to compare two different models: the occlusion of the circumflex coronary artery (Cx) vs the occlusion of the left anterior descending coronary artery (LAD). METHODS Each group consisted of 10 New Zealand rabbits; after 50 minutes of occlusion the artery was reopened for 20 minutes and then a biopsy from the area at risk and another from the perfused area were obtained. The specimens were used for chemiluminiscence and electron microscopy. Electrocardiograms were taken throughout the experience. Transverse sections of both ventricles were used for light microscopy. RESULTS In both groups elevations of the ST segment, more important in the Cx group (p < 0.001) were observed. In the LAD group, the QRS complexes were enlarged in three animals, in 4 rabbits there were reperfusion arrhythmias, but the experimental mortality was zero. In the other group, 50% of the animals died during the experiment. In the LAD group the chemiluminiscence of the area at risk was greater than that of the perfused area (p < 0.001). No differences could be demonstrated between the samples of the Cx group, probably because of the extensive necrotic areas unable to generate photoemission. Ultrastructural and microscopic characteristic lesions of the ischemia-reperfusion phenomena were found in both groups, particularly severe in the Cx group with extensive areas of necrotic tissue. CONCLUSIONS This experience shows that the myocardial necrosis, the mortality and the malignant arrhythmias were quantitatively different according to which coronary artery was occluded. This fact may be taken into account when an animal model for ischemia-reperfusion is selected.