We use a comparative approach to study the cellular and subcellular molecular mechanisms regulating energy metabolism, mitochondrial respiration and consequences for cardiovascular function in vertebrates, with focus on hypoxia tolerant species. We also study the regulation of protein synthesis in response to digestion, cellular regulation of contractile function in cardiac cells. We study physiological function and evolution of oxygen carrier globin proteins (hemoglobin in the blood and myoglobin in the heart), signalling functions of NO and H2S ‘gasotransmitters’ in controlling metabolic depression, and their interactions with globins and other proteins, and the regulation of mitochondrial respiration and of reactive oxygen species following oxygen deprivation. These studies are performed using several techniques such as high-resolution respirometry for cells and mitochondria and custom-made diffusion chamber for the analysis of oxygen binding curve of globin proteins. The effects of toxic compounds is also a topic of research.