Blood flow through the body is slow. Amphibians See drawing on board. Returns to the heart for second push before going to the body. Blood flow in body is faster than in fish. In the ventricle, oxygenated blood returning from the lungs mixes with deoxygenated blood returning from the body.
Amphibian metabolism is relatively low.
Interior of ventricle directs flow. Reptiles, Birds, Mammals Much higher metabolism Body covered with scales, feathers, fur Cannot tolerate mixing in ventricle. Four-chambered heart See drawing. The 2 atria contract before the 2 ventricles. Wave of contraction Spreads from SA node across the two atria.