The heart is obliged to contract continuously. This implicates for a human with an average heart rate of 70 beats per minute in about 70 years more than 2.5 billions of contractions. For this contraction ATP is needed as the main substrate. As a consequence continuous ATP production by the heart is obligatory. This ATP is mainly produced by the oxygen-dependent oxidative phosphorylation. Disturbances of the oxygen delivery, such as that induced by partial occlusion of one or more coronary arteries can lead to a distortion of the balance between ATP production and consumption. As a res11lt, ATP is dephosphorylated, and subsequently the products adenosine, inosine, hypoxanthine, xanthine and uric acid pass the cellular membrane and appear in the coronary effluent. Because of the importance of adequate ~TP levels for the heart, the following 4 main ::.\'Venues have been investigated in this study, which forms the substance of my thesis.