We aim to track mesenchymal stem cells (MSCs) after magnetically labeling and test the ability of these cells differentiate into cardiomyocytes in vivo. Therefore, 20 swines were divided into four groups, sham-operated group (n=3); acute myocardial infarction (AMI) transplanted with PBS (n=3); labeled MSCs (n=7) and unlabeled MSCs (n=7) group. 10(7) labeled or unlabeled cells were intracoronary delivered after MI (4.8+/-1.3 days), and serial cardiac MR (3.0T) imaging studies were performed at 0, 4 and 8 weeks after transplantation, then the results were confirmed by histological and western blot analysis. We demonstrated that labeled MSCs can be reliably detected and tracked in vivo using MR imaging. In particular, we provided the evidence of regeneration of labeled MSCs in vivo by histological examination and western blot analysis.