The aim of the present trial from China was to evaluate the role of beta-blocker, metoprolol compared with placebo among patients with ST elevation myocardial infarction (MI) presening within 24 hours of symptom onset. Patients undergoing primary angioplasty and with systolic blood pressure <100 mmHg, heart rate <50 beats per minute (bpm), or II/III degree atrioventricular (AV) block were excluded. Patients were randomized to treatment with metoprolol (3 intravenous injections of 5 mg each followed by oral 200 mg/day for up to 4 weeks; n=22928) or placebo (n=22923). All patients were also given aspirin 162 mg/ day. Patients were also randomized in a factorial design to treatment with clopidogrel or placebo. Fibrinolytic therapy was used in 50% of patients and anticoagulants in 74% patients. Baseline characteristics were comparable between the two treatment groups. Anterior infarction was present in 50% of patients. First intravenous injection of study drug treatment was given in 98.5% of patients in the metoprolol group and 98.6% in the placebo group and all three injections were given in 90.2% and 96.0%, respectively. Oral treatment was completed in 86.2% and 91.6%, respectively. There was no difference in the primary endpoint of death, reinfarction or cardiac arrest by treatment group at hospital discharge/4 weeks (9.5% for metoprolol v. 9.9% for placebo, p=NS). There was also no difference in the co-primary endpoint of all-cause mortality by hospital discharge (7.7% v. 7.8%, p=NS). Reinfarction was lower in the metoprolol group (2.0% v. 2.5%, p=0.002). Ventricular fibrillation occurred less frequently in the metoprolol group (2.5% v. 3.0%, p<0.001) but there was no difference in other cardiac arrests (3.8% v. 3.9%, p=NS). Death due to shock occurred more frequently in the metoprolol group (2.2%, n=496 v. 1.7%, n=384), while death due to arrhythmia occurred less frequently in the metoprolol group (1.7%, n=388 v. 2.2%, n=498). Cardiogenic shock was overall higher in the metoprolol group (5.0%, n=1141 v. 3.9%, n=888, p<0.0001), particularly early in the treatment period (2.1% v. 1.4% on day 0) and among patients with Killip class II (7.9% v. 6.5%) or class III (16.2% v. 10.4%). Among patients with ST elevation MI, treatment with metoprolol was not associated with a reduction in the primary endpoints of death, reinfarction or cardiac arrest compared with placebo. There was a reduction in reinfarction in the metoprolol group. However, cardiogenic shock and death from shock occurred more often in patients treated with metoprolol specially in those with reduced left ventricular function, as demonstrated by the Killip class. Additionally, the risk was largest early in the treatment period on days 0 and 1, suggesting that intravenous therapy during the acute phase of the infarction should be avoided.