Inadequate myocardial tissue perfusion despite successful relief of the culprit occlusion and restoration of epicardial coronary flow for ST-segment elevation acute myocardial infarction (STEMI) results in poor outcome. The investigators hypothesized that nitroprusside (NTP) injected intracoronary immediately before angioplasty might prevent no-reflow and improve vessel flow and myocardial perfusion.