 The primary aim of the current study is a better understanding of the role of Type 2 Diabetes Mellitus T2DM in heart failure and, in particular, changes in cardiac metabolism, which may contribute to heart failure. Various biomarkers in the coronary artery blood, as well as in the arterial and peripheral venous blood, are to be identified for this purpose. Included are patients with and without T2DM, who have a clinically indicated and guidance-appropriate Cardiac Resynchronisation Therapy CRT implantation due to their cardiac insufficiency. 