Inclusion Criteria:  informed patient consent patient scheduled for an elective cardiac surgery. The following procedures are accepted: coronary artery bypass grafting (CABG) , single valve replacement (SVR), CABG + SVR, CABG + MAZE procedure, SVR + MAZE procedure  Exclusion Criteria:  complex cardiac surgery (except the options listed above) ejection fraction of the left ventricle < 30 % according to the last preoperative echocardiography EuroSCORE II value > 5 % urgent or emergent surgery patient unable to walk and/or perform the test severe dementia (due to unability to cooperate during the testing and follow-up) re-do surgery minimally invasive surgery (i.e. other than full median sternotomy)