 The degree of mixing of oxygenated and deoxygenated blood in the three-chambered heart varies depending on the species and physiological state.Under different conditions, deoxygenated blood can be shunted back to the body or oxygenated blood can be shunted back to the lungs.This variation in blood flow has been hypothesized to allow more effective thermoregulation and longer diving times for aquatic species, but has not been shown to be a fitness advantage.