AIM:To explore the protective effect of ischemic preconditioning on myocardial capillary bed. METHODS: Anesthetized open-chest dogs in ischemic preconditioning (IP) group ( n =6) were subjected to 5 min ischemia and 5 min reperfusion for 4 times in left descending coronary artery (LDA) while the dogs in sham-operated (SO) group ( n =6) were observed for 40 min without any stimulating. Myocardial contrast echocardiography (MCE) was performed before the surgery, at the end of the first and the fourth ischemia and reperfusion period, respectively. Myocardial samples in ischemic area were obtained for capillaries ultrastructure examination and their quantitative analysis was conducted by corresponding imagine analyzing system, then compared within group and between control group. RESULTS: (1) Comparing fourth 5 min ischemia with first one, the percents of area defect in minimum (AD min%) by MCE decreased from 32.6%?5.7% to 21.8%?5.2%( P