 Right atrial samples obtained from patients undergoing cardiac surgery and presenting no sign of clinical cardiomyopathy will be grouped according to patients body mass index. Atrial trabeculae will be explored to dissect out the respective contribution of i sarcoplasmic reticulum dysfunction isometric twitch force contraction analysis, ii abnormal sarcomere sensitivity to calcium assessed in permeabilized fibers and iii mitochondrial dysfunction to intrinsec contractile dysfunction of myocardium in obese patients. 