Animals are exposed to natural and anthropogenic environmental stresses that affect animal life at all levels of biological organization, from molecules and cells to organs, individuals, and populations. We study the physiological adaptation and acclimation of ectothermal animals, mainly fish, and their adaptation to abiotic environmental conditions in the northern and arctic regions. In particular, the effects of temperature and oxygen availability on the cardiovascular function of fish under seasonally changing conditions are investigated. Our research topics include thermal adaptation and acclimation of fishes, the use of zebrafish as an animal model in thermal biology of ectotherms and human cardiac electrophysiology, and combined effects of thermal stress and environmental toxicants on fish cardiovascular function.