- Objectives This study sought to determine whether alginate biomaterial can be delivered effectively into the infarcted myocardium by intracoronary injection to prevent left ventricular (LV) remodeling early after myocardial infarction (MI). Background Although injectable biomaterials can improve infarct healing and repair, the feasibility and effectiveness of intracoronary injection have not been studied. Methods We prepared a calcium cross-linked alginate solution that undergoes liquid to gel phase transition after deposition in infarcted myocardium. Anterior MI was induced in swine by transient balloon occlusion of left anterior descending coronary artery. At 4 days after MI, either alginate solution (2 or 4 ml) or saline was injected selectively into the infarct-related coronary artery. An additional group (n = 19) was treated with incremental volumes of biomaterial (1, 2, and 4 ml) or 2 ml saline and underwent serial echocardiography studies. Results Examination of hearts harvested after injection showed that the alginate crossed the infarcted leaky vessels and was deposited as hydrogel in the infarcted tissue. At 60 days, control swine experienced an increase in left ventricular (LV) diastolic area by 44%, LV systolic area by 45%, and LV mass by 35%. In contrast, intracoronary injection of alginate (2 and 4 ml) prevented and even reversed LV enlargement (p Conclusions Intracoronary injection of alginate biomaterial is feasible, safe, and effective. Our findings suggest a new percutaneous intervention to improve infarct repair and prevent adverse remodeling after reperfused MI.