Abstract: Objective To observe the effect of primary percutaneous coronary intervention (PCI) on plasma B-type natriuretc peptide (BNP) in patients with acute myocardial infarction (AMI). Methods Thirty-eight patients with AMI were divided into two groups for PCI (n=26) and conventional treatment (n=12). The plasma BNP levels were measured by fluorescence immunoassay (FIA) in these patients immediately, 24 h, 7 d, and 30 days after admission, and the infarct-related coronary arteries (IRA) were treated only with emergency interventional therapy in PCI group. Results BNP of the patients in the PCI and conventional treatment group B increased immediately and 24 h after admission, but there was no significant difference between the two groups (243.74±75.68 vs 228.65±82.32 and 283.42±88.66 vs 275.48±89.67, P>0.05). BNP in PCI group decreased but that in conventional treatment group increased 7 days after admission, showing significant difference between them (203.63±59.42 vs 388.74±108.52, P<0.05 ). BNP remained significantly lower in the PCI group than in the other group 30 days after admission (96.31±43.22 vs 237.66±75.48, P<0.01). Emergency PCI for different IRA resulted in the significant difference in BNP between the patients, and intervention of the left anterior descending artery (LAD) resulted in more obvious BNP reduction in comparison with that due to interventional of the right coronary artery (RCA) and left circumflex coronary artery (LCX). The changes in left ventricular ejection fraction (LVEF) and left ventricular end-diastolic dimension (LVEDD) were correlated to the changes of BNP. The mean BNP in the 3 fatal cases was nearly 10-fold higher than the normal level. Conclusions BNP of AMI patients decreases on days 7 and 30 after reperfusion therapy with primary PCI, and the reduction can be more obvious 30 days after admission.