Twenty hospitals in Japan will participate in the J-WIND-ANP study. Patients with AMI who are candidates for PCI are randomly allocated to receive either intravenous ANP or placebo administration. The primary end-points are (1) estimated infarct size (Σcreatine kinase and troponin T) and (2) left ventricular function (left ventriculograms). Single nucleotide polymorphisms (SNPs) that may be associated with the function of ANP and susceptibility of AMI will be examined. Furthermore, a data mining method will be used to design the optimal combinational therapy for post-MI patients.