BACKGROUND: Bioabsorbable cardiac matrix (BCM) is a novel device that attenuates adverse left ventricular (LV) remodeling after large myocardial infarctions in experimental models. OBJECTIVES: This study aimed to analyze whether BCM, compared with saline control, would result in less LV dilation and fewer adverse clinical events between baseline and 6 months. METHODS: In an international, randomized, double-blind, controlled trial, 303 subjects with large areas of infarction despite successful primary percutaneous coronary intervention (PCI) of ST-segment elevation myocardial infarction (STEMI) were randomized 2:1 to BCM or saline injected into the infarct-related artery 2 to 5 days after primary PCI. The primary outcome was mean change from baseline in LV end-diastolic volume index (LVEDVI) at 6 months. Secondary outcomes included change in Kansas City Cardiomyopathy Questionnaire score, 6-minute walk time, and New York Heart Association functional class at 6 months. The primary safety endpoint was a composite of cardiovascular death, recurrent MI, target-vessel revascularization, stent thrombosis, significant arrhythmia requiring therapy, or myocardial rupture through 6 months. RESULTS: In total, 201 subjects were assigned to BCM and 102 to saline control. There was no significant difference in change in LVEDVI from baseline to 6 months between the groups (mean change ± SD: BCM 14.1 ± 28.9 ml/m(2) vs. saline 11.7 ± 26.9 ml/m(2); p = 0.49). There was also no significant difference in the secondary endpoints. The rates of the primary safety outcome were similar between the 2 groups (BCM 11.6% vs. saline 9.1%; p = 0.37). CONCLUSIONS: Intracoronary deployment of BCM 2 to 5 days after successful reperfusion in subjects with large myocardial infarction did not reduce adverse LV remodeling or cardiac clinical events at 6 months. (IK-5001 for the Prevention of Remodeling of the Ventricle and Congestive Heart Failure After Acute Myocardial Infarction [PRESERVATION I]; NCT01226563).