OBJECTIVE To evaluate whether satellite cells injected into infarct areas in rabbits remain viable during 6 weeks follow-up and can improve cardiac function as assessed by echocardiography. METHODS Myocardial infarction was induced in 16 New Zealand white rabbits, by ligation of the marginalis sinistra artery. Tissue from gluteus muscle biopsies was dissected into small pieces and cultured. Within 2-3 weeks the cells were expanded by 2-3 orders of magnitude and were fluorescent labeled. Single cell pellets for resuspension at >10(6)/1 ml were directly injected into the infarct areas in 8 rabbits. In 8 additional rabbits, 1 ml saline was injected (control). Regional left ventricular function was assessed weekly by 2-D echocardiography until animals were sacrificed. Analysis was performed blind and independently by two experienced echocardiographers, based on the American Society of Echocardiography scheme. CONCLUSIONS Six treated and five control rabbits completed the study. One week after the artery occlusion, left ventricular function scoring did not differ between groups, mean 8.7+/-1.6 vs 8.3+/-1.9 (P=0.74). At 6 weeks post-injection, echocardiographic score was significantly better in the treated group, mean 2.6+/-0.9 vs 6.9+/-2.1 (P=0.002). The treated group showed significant gradual segmental improvement between the first week up to week 6. After sacrifice, macro and microscopic transmural areas showed typical changes of myocardial infarction. Histochemical staining identified viable grafted cells in high density 6 weeks post-transplantation in all grafted hearts. CONCLUSIONS Autologous satellite cells (skeletal myofiber), can be successfully grafted into rabbit hearts following myocardial infarction and may induce improved regional left ventricular function.