To assess the safety and efficacy of transendocardial delivery of muscle‐derived stem/progenitor cells with connexin‐43 overexpression (Cx‐43‐MDS/PC) in advanced heart failure (HF).

Thirteen subjects with advanced HF, New York Heart Association (NYHA) class II–III were enrolled and treated with targeted injection of Cx‐43‐MDS/PCs and then monitored for at least 6 months. Overexpression of Cx43 (Cx43+) was significantly higher in all but one subject (Cx43–). Injection of MDS/PCs was associated with significant improvement of exercise capacity: NYHA (3 ± 0 vs. 1.8 ± 0.7, P = 0.003), exercise duration (388.69 ± 141.83 s vs. 462.08 ± 176.69 s, P = 0.025), peak oxygen consumption (14.38 ± 3.97 vs. 15.83 ± 3.74 ml/kg.min, P = 0.022) and oxygen pulse (10.58 ± 2.89 vs. 18.88 ± 22.63 mLO₂/heart rate, P = 0.012). Levels of BNP, left ventricular (LV) ejection fraction and LV end‐diastolic volumes tended to improve. There was a significant improvement of the mean unipolar voltage amplitudes measured for the injected segments and the entire left ventricle (9.62 ± 2.64 vs. 11.62 ± 3.50 mV, P = 0.014 and 8.83 ± 2.80 vs. 10.22 ± 3.41 mV, P = 0.041, respectively). No deaths were documented, Cx43+ (n = 12) subjects presented no significant ventricular arrhythmia; one Cx43– subject suffered from ventricular tachycardia (successfully treated with amiodarone).

Injection of Cx‐43‐MDS/PCs in patients with severe HF led to significant improvement in exercise capacity and myocardial viability of the injected segments while inducing no significant ventricular arrhythmia. This may arise from improved electrical coupling of the injected cells and injured myocardium and thus better in‐situ mechanical cooperation of both cell types. Therefore, further clinical studies with Cx43+ MDS/PCs are warranted.