The benefit of using subcutaneous low molecular weight heparin for the treatment of acute myocardial infarction is not known. The aim of this study was to determine the efficacy of a low molecular weight heparin (dalteparin sodium) for the treatment of acute myocardial infarction in patients not treated with thrombolytic therapy. Twenty-nine cardiological centres from leading hospitals in India participated in this prospective, multicentre, double-blind, placebo-controlled study in two phases which included 1128 patients with acute myocardial infarction. In the acute phase (between day 1 and 3 of admission) all the patients received a weight-adjusted dose of subcutaneous dalteparin (120 IU/kg twice daily). In the second, double-blind phase of acute myocardial infarction, patients were randomised to receive a fixed dose of dalteparin (7,500 IU) or an identical placebo injection for 30 days. A composite primary endpoint of death, reinfarction, recurrence of angina and emergency revascularisation was used. All the 1128 patients with acute myocardial infarction were included in the trial. In the acute phase, the composite primary endpoint was observed in 58 (5.1%) patients. Of 1037 paients who were randomly assigned to receive a fixed dose of dalteparin (n=519) or placebo (n=518), the composite primary event rate was 6.7 percent and 7.0 percent, respectively (RR 0.97; 95% CI 0.62-1.52; p=0.90). To conclude, treatment with dalteparin administered subcutaneously in a weight-adjusted dose of 120 IU/kg twice daily resulted in a lower than expected mortality during the acute phase of myocardial infarction. A lower fixed once daily dose of 7,500 IU during the chronic phase did not confer additional protection.