The objective was to examine the changes in the capillary network in the left ventricle of rats subjected to transient occlusion of the left coronary artery followed by reperfusion (I-R). Eighteen Wistar rats were divided into three groups and all rats were anaesthetized with ethyl ether and artificially ventilated. The I-R 1 rats were subjected to a 3 min occlusion followed by reperfusion; the I-R 3 rats had three 3 min occlusions separated by 3 min of reperfusion; the Sham-operated rats underwent surgery but the coronary artery was not occluded. The thorax was closed at the end of the procedures and the rats were sacrificed for isolation of the hearts 30 d after treatment. Frozen sections of the left ventricles were cut and differential staining was used to classify the capillary portions. Five additional rats treated as the I-R 1 group were sacrificed at 120 min after reperfusion. Their left ventricles were used for immunohistochemical investigation of the early expression of bFGF and VEGF. By comparison with the Sham-operated rats, both I-R groups showed increases in the capillary density of total and venular capillary portions, an increased capillary : myocyte (C : M) ratio and a decrease in the capillary domain area in the three capillary portions. The changes in the I-R 1 group were significantly greater than those in the I-R 3 group, suggesting that the frequent experience of ischemic attack reduces the capacity of angiogenesis. In the rats sacrificed 120 min after the start of reperfusion, bFGF and VEGF were expressed on capillaries and in some myocytes. Punctate bFGF or VEGF staining was observed even 30 d after the transient ischemia. One 3 min occlusion of the left coronary artery followed by reperfusion produced changes in capillarity that would increase the oxygen supply to ventricular tissues. These effects may be attributed to the bFGF and VEGF expressed around capillaries. Repeated occlusions interspersed with a short period of reperfusion reduced the advantageous effects on capillarity.