Cardiac scope in amphibians: transition to terrestrial life

Systemic oxygen transport essentially limits maximal aerobic capacity in amphibians and consequently may be an important determinant of aerobically supported behaviors. Exercise widens arteriovenous oxygen content difference (5×) and increases heart rate (2×), whereas stroke volume changes very little over resting values. Dehydration is the primary problem facing amphibians in the transition to terrestrial life. Dehydration influences cardiac scope by imposing hyperosmotic, hypovolemic, and hyperviscous stresses on cardiac function. The ability to compensate for hypovolemic stress is the principal adaptation sustaining cardiac scope in more dehydration-tolerant amphibians.