['The relationship between platelet activity and myocardial injury in patients with ST-segment elevated (ST-se) acute myocardial infarction (AMI) remains unclear. This study tested the hypothesis that platelet activity (expressed by CD62p) is enhanced and predictive of both the extent of myocardial damage and 30-day clinical outcome in patients with ST-se AMI undergoing primary coronary stenting.', 'Platelet CD62p expression prior to coronary angiographic was prospectively measured using flow cytometry in 45 consecutive patients with AMI undergoing primary coronary stenting. The CD62p expression was also evaluated in 20 healthy and 20 at-risk control subjects. The CD62p expression was significantly higher in AMI patients than in healthy and at-risk control subjects (all p values <0.0001). Patients with high CD62p expression (>or=8%) had significantly higher creatine kinase-MB (p<0.0001) levels, higher incidence of cardiogenic shock (p=0.009) upon presentation, significantly lower left ventricular ejection fraction (p=0.0003), and significantly higher incidence of 30-day composite major adverse clinical outcomes (MACO) (advanced congestive heart failure >or=class 3 or 30-day mortality) (p<0.0001) than those patients with low CD62p expression (<8%). Multiple stepwise logistic regression analysis demonstrated that only high CD62p expression (>or=8%) was an independent predictor of 30-day MACO (all p<0.0001).'] Is platelet activity a biomarker of cardiac necrosis and predictive of untoward clinical outcomes in patients with acute myocardial infarction undergoing primary coronary stenting?