BACKGROUND - Skeletal myoblast (SM) transplantation (Tx) in a post-myocardial infarction (MI) scar experimentally improves left ventricular (LV) ejection fraction (EF). Short-term follow-up (FU) studies have suggested that a similar benefit could clinically occur despite an increased risk of LV arrhythmias. METHODS AND RESULTS - We report the long-term FU of the first worldwide cohort of grafted patients (n =9, 61.8±11.6 years, previous MI, EF ≤35%) operated on (autologous SM Tx and bypass surgery) in 2000 to 2001 and evaluated before Tx, at 1 month (M1) and at a median FU of 52 (18 to 58) months after Tx (37 patient-years). NYHA class improved from 2.5±0.5 to 1.8±0.4 at M1 (P=0.004 versus baseline) and 1.7±0.5 at FU (P=not significant versus M1; P=0.0007 versus baseline). EF increased from 24.3±4% to 31±4.1% at M1 (+28%, P=0.001 versus baseline) and remained stable thereafter (28.7±8.1%, +18% versus baseline). There were 5 hospitalizations for heart failure in 3 patients at 28.6±9.9 months, allowing implant in 2 patients with a resynchronization pacemaker. An automatic cardiac defibrillator (ACD) was implanted in 5 patients for nonsustained (n =1) or sustained (n =4) ventricular tachycardia at 12.2±18.6 (1 to 45) months. Despite a beta-blocker/amiodarone combination therapy, there were 14 appropriate shocks for 3 arrhythmic storms in 3 patients at 6, 7, and 18 months after ACD implantation. CONCLUSIONS - In this cohort of severe heart failure patients both clinical status and EF stably improve over time with a strikingly low incidence of hospitalizations for heart failure (0.13/patient-years) and the arrhythmic risk can be controlled by medical therapy and/or on-request ACD implantation. © 2006 American Heart Association, Inc.