Introduction and objectives Late contrast-enhanced cardiac magnetic resonance (CMR) enables areas of persistent microvascular obstruction (PMO) to be detected early after acute myocardial infarction. Our aim was to evaluate the impact of PMO on subsequent ventricular remodeling in a cohort of patients with acute ST-elevation myocardial infarction (STEMI) who underwent intracoronary autologous bone-marrow mononuclear cell (ABMMC) transplantation. Methods In total, 14 patients underwent intracoronary transplantation of 66±39×106 ABMMCs 8±2 daysfollowing successful revascularization of a STEMI (i.e., TIMI flow grade 3 in the affected artery). Serial CMR studies with gadolinium-DTPA enhancement were performed at baseline and 10 months after infarction. Left ventricular volume and ejection fraction, regional contractility and the infarct size were measured and the presence of PMO (defined as hypoenhanced areas within the infarcted zone) was investigated. Results Overall, PMO was detected in five of the 14 patients (36%). Those with PMO tended to have a larger infarct size, larger ventricular volumes, and poorer regionaland global left ventricular systolic function in baseline studies than those without PMO. At follow-up, there were significant associations between PMO and an increase in end-diastolic volume (25±24 mL vs. −2±19 mL; P=.037), the absence of an increase in end-diastolic parietal thickness (P=.027), and a smaller reduction in the number of akinetic or dyskinetic segments. Conclusions The detection of PMO by CMR early after successful revascularization of a STEMI in patients who underwent intracoronary ABMMC transplantation was associated with adverse left ventricular remodeling.