The heart is not just the motor of blood circulation. It is also an endocrine organ that produces hormones or messenger substances that are released into the bloodstream and thus can influence the entire body. This function of the heart is often neglected and little researched. We were able to detect a protein in heart muscle cells that is a marker for endocrine cells, and we have confirmed that the heart has properties of an endocrine organ. A calcium-dependent signal cascade that leads to the release of hormones is only known in neuro- / endocrine cells. Put simply, a stimulus arrives in the cell (“excitation”) and subsequently leads to the release of hormones (“secretion”). We hypothesize that this type of hormone release also exists in heart muscle cells, contributing to "Excitation-secretion coupling". The aim of the work is to understand the effect of different stimuli on the secretion of hormones, such as natriuretic peptides, and the underlying mechanisms. In this way, it may be possible in the future to intervene in the mechanism to regulate it and develop new treatment strategies for cardiac insufficiency.