Mitochondria are ubiquitous organelles of eukaryotic cells and they are the mayor site of generating energy in the form of adenosine triphoshate through the process of oxidative phosphorylation. Analysis and estimation of mitochondrial function is of outmost importance when it comes to studying intracellular energy metabolism, mechanisms of apoptosis, signaling pathways, calcium storage and the pathophysiology of a large spectrum of human diseases including various neurodegenerative diseases, myopathies, metabolic syndromes and cancer. Respiratory capacity analysis covers one of the many roles that mitochondria play in living cells and it provides us with useful data about functional integrity of mitochondria. Assessment of individual respiratory chain complexes or other mitochondrial enzymes has been widely used to estimate mitochondrial function and dysfunction but it neglects the influence of complex structural and functional interplay of mitochondrial proteins and enzymes and plasmic compounds. Another method that emphasises the importance of studying intact mitochondria is in vitro technique, and although it has many advantages, in some aspects it is far from being representative when it comes to functional assessment of mitochondria. From the perspective of energy production and consumption, the cardiac muscle is a highly demanding tissue and it is the well functioning of mitochondria that is conditio sine qua non for this nature to be fulfilled. In cooperation with the University of Split School of Medicine in Split and under the mentorship of Prof. Marko Ljubkovic, the Department of Physiology of the Faculty of Medicine Novi Sad works on introducing in situ approaches in the analysis of respiratory mitochondrial function in skinned muscle fibers of human cardiac tissue.