In the current era, up to 30% of patients with ST-segment elevation myocardial infarction, usually those presenting late, show ongoing left ventricular (LV) remodeling and poor clinical outcome despite primary percutaneous coronary intervention (PCI). Cardiac transfer of bone marrow-derived stem and progenitor cells has been investigated as an adjunctive therapy to promote regeneration of infarcted myocardium. Therefore, we designed a multicenter, randomized study to test the safety and efficacy of intracoronary injection of autologous BMNCs in patients with large acute anterior myocardial infarction and late presentation, who were treated with successful primary PCI.