Male (NZW x BXSB)F1 mice ([W x B]F1) were used as a model for small coronary artery disease. The mortality rate for 162 mice was 0% at 12 weeks and 37% at 24 weeks. The incidence of myocardial infarction (MI) was 0% at 12 weeks, 22% at 16 weeks, 39% at 20 weeks, and 53% at 24 weeks. In 29 of the 35 (W x B)F1 male mice with MI, small multiple infarctions were noted in the right ventricular free wall and anterior, lateral, posterior, and septal ventricular walls. In 25 of the 29 hearts with multiple infarcts, the infarcts in the same heart were at the same histologic stage. Twenty-one of these hearts showed only replacement fibrosis, and 4 hearts showed only granulation. The remaining 4 hearts with multiple infarcts exhibited coagulation necrosis plus fibrosis or granulation. Quantitative analysis of the infarct size revealed that in the 35 (W x B)F1 males with MI, the relative area of MI (%MI) was significantly larger in the right ventricular free wall (6.7% +/- 8.4%) than in the ventricular septum (1.9% +/- 2.4%) or in the left ventricular free wall (2.1% +/- 2.5%). The %MI was greatest in the right third (3.6% +/- 5.4%) of the ventricular septum and in the outer third (2.9% +/- 3.3%) of the left ventricular free wall. The %MI did not increase with age. In 11 of the 35 (W x B)F1 mice, 27 intramural small arteries showed marked obliterative lesions. Most of them were in the right ventricular free wall, the right third of the ventricular septum, or the outer third of the left ventricular free wall. There was no evidence of stenosis in the extracardiac major coronary arteries. In addition, the infarct showed a whirlpool-like configuration, and x-ray photographs revealed that the small intramural coronary arteries had a whirlpool-like configuration. It is concluded that in (W x B)F1 males multiple small infarcts appear at the same time due to small coronary artery disease. The whirlpool configuration of the infarct reflects the special anatomy of the intramural coronary arteries in the mice.