Intramyocardial cell grafting aims to limit the consequences of the loss of contractile function of a damaged left ventricle. Its functional efficacy is suggested by a wealth of experimental data using multiple evaluation techniques in different animal species. Intramyocardial injections of cultured fetal cardiomyocytes after infarction increase the ejection fraction. Cultured autologous skeletal myoblasts, which do not raise immunologic, ethical, tumorigenesis, or donor availability problems, improve ventricular function to a similar extent. The presence of connexin-43 is demonstrated between fetal (but not myoblast) grafted cells and host myocytes. Thus, the mechanisms of this beneficial effect (direct systolic effect, paracrine factors, passive girdling effect, and decrease in wall stress) remain controversial. These encouraging results have opened the way to the first clinical trial in patients with low ejection fractions, akinetic and nonviable postinfarction scars, and indications for coronary artery bypasses in remote, viable, and ischemic areas. Large-scale cell expansion allows a yield of >10 9 myoblasts from a single human muscular biopsy. Cultured autologous myoblasts are directly administered by multiple injections within and around the infarcted area during open-chest surgery. Preliminary postoperative observations show an improvement in ejection fraction, reappearance of a systolic thickening of the grafted scars, and a new-onset metabolic viability within this area. Thus, this new procedure might become a useful adjunct to current treatments of severe ischemic heart failure.