Differences in heart rate, stroke volume, cardiac output, and cardiac index between the hibernating and active states of free-ranging brown bears. First row shows repeated measurements from each bear, second row shows mean values and standard deviations. Levels of significance: *P < 0.05, **P < 0.01 and ***P < 0.001. During hibernation, all assessed hemodynamic parameters were significantly decreased as an adaptation to low energy demands. During hibernation, the cardiac index, which is cardiac output related to body size, had a level that would imply very severe cardiogenic shock in humans and, thus, would be largely incompatible with life.