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To study the effects of B-type natriuretic peptide (BNP) preconditioning on the apoptosis and expressions of Bcl-2 and Bax in rat cardiomyocytes during myocardial ischemia-reperfusion.Twenty-one male Sprague-Dawley rats weighing (250 ± 50) g were randomly divided into 3 groups of sham operation (SHAM), ischemia-reperfusion (I/R) and B-type natriuretic peptide (BNP). A rat model of in vivo myocardial ischemia-reperfusion injury was established by ligating the left anterior descending coronary artery for 35 minutes and then reperfusing for 240 minutes. The apoptosis of myocardial cell was determined by terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end-labeling (TUNEL) method. Real-time polymerase chain reaction and Western blot were used to detect the expression changes of Bcl-2 and Bax in rat ischemia myocardium.The apoptotic indices of SHAM, BNP and I/R groups were 5.4% ± 4.2%, 22.5% ± 9.5% and 45.2% ± 13.0% respectively (P0.05). The Bcl-2 protein expression of SHAM, BNP and I/R groups were 0.87 ± 0.09, 0.70 ± 0.07 and 0.38 ± 0.09 respectively (P0.05). The Bax protein expression of SHAM, BNP and I/R groups were 0.08 ± 0.04, 0.39 ± 0.09 and 0.71 ± 0.18 respectively (P0.01). The Bcl-2/Bax mRNA ratio of SHAN, BNP and I/R groups were 0.763 ± 0.154, 0.099 ± 0.025 and 0.022 ± 0.024 respectively (P0.05).The BNP preconditioning can decrease the myocardial apoptosis induced by ischemia-reperfusion injury. The mechanisms may be associated with an elevated expression of Bcl-2, an increased ratio of Bcl-2/Bax and a lowered expression of Bax.