Cardiovascular disease (CVD) with ischemic heart disease as the main contributor is the major cause of death worldwide, accounting for more than 30% of all deaths each year [
1]. Therefore, it is of tremendous interest to reduce the consequences of CVD, i.e. myocardial ischemia reperfusion (I/R) injury and its subsequent morbidity and mortality. Transient ischemic episodes of peripheral tissue increases the tolerance of the myocardium against a subsequent I/R injury [
2]. This phenomenon is called remote ischemic preconditioning (RIPC). RIPC is considered to be an easy to use and inexpensive technique for protecting the heart against I/R injury in many clinical situations [
3]. For example, a recent meta-analysis of 13 randomized clinical trials showed a benefit of RIPC in patients with acute myocardial infarction [
4]. Although RIPC has been shown to be effective in both animal studies and humans, there are increasing concerns of its protective potential in the clinical arena. To date, two very recent, large-scale clinical trials (ERICCA and RIPHeart) failed to show the effectiveness of RIPC in heart surgery patients [
5,
6]. The reason for this discrepancy remains unclear, but there is strong evidence that cardioprotective interventions, e.g. ischemic preconditioning, are affected by numerous factors including age and sex [
7,
8]. However, there is only limited information whether both aging and sex also interfere with the protective potential of RIPC. With respect to aging, a sub-group analysis of the ERICCA trial did not indicate age as confounding factor for RIPC [
5]. In contrast, a meta-analysis of Zhou et al. showed a reduced incidence of acute kidney injury after RIPC, and this effect was more pronounced in younger patients [
9]. In addition, our group demonstrated recently, that the protective effect of RIPC is lost in the aged heart using an experimental in vivo rat model [
10]. However, it is unclear which mechanisms might be accountable for the potential loss of protection by RIPC. On the one hand, there might be disorders in signal transduction between the remote organ and the effector organ (i.e. a modification in the release of the humoral factors); on the other hand, there might be structural changes of the protecting signalling pathway within the heart leading to possible age- and sex-dependent loss of cardioprotection by RIPC. To gain insight into the mechanism by which aging, and possibly sex, interfere with RIPC, we used a mixed experimental approach with RIPC induction in humans and the isolated heart model as bioassay to test the hypothesis that the release of humoral factor(s) after RIPC is affected both increasing age and sex.