How does the three-chambered heart equip amphibians for life on land?

The frog's three-chambered heart more efficiently delivers oxygen to body cells as compared to the fish's two chambered heart. As compared to a four-chambered heart, the frog's three-chambered heart allows blood to bypass the lungs when the lungs are not functioning in gas exchange.

In the three-chambered heart of amphibians, one chamber receives blood from the lungs and another receives blood from THE REST OF THE BODY, INCLUDING THE SKIN. Blood from both chambers then moves to the third chamber, which pumps blood back to the lungs, skin, and rest of the body. This results in some mixing, BUT EXPERIMENTS USING DYES HAVE SHOWN THAT BLOOD PUMPED TO THE LUNGS AND SKIN COMES PRIMARILY FROM THE SKIN AND THE REST OF THE BODY AND BLOOD PUMPED TO THE HEAD COMES PRIMARILY FROM THE LUNGS. BLOOD PUMPED TO THE REST OF THE BODY IS A MIXTURE OF OXYGEN-POOR BLOOD FROM THE REST OF THE BODY AND BLOOD FROM THE SKIN AND LUNGS, WHICH CARRIES OXYGEN. IHOWEVER, in amphibians, the skin is much more important than the lungs as an organ for gas exchange, especially when the frog is under water. THE LACK OF TOTAL SEPARATION OF THE BLOOD IN THE HEART ALLOWS BLOOD TO DETOUR AROUND THE LUNGS WHEN THE FROG IS UNDER WATER. AS COMPARED TO A TWO-CHAMBER HEART, DOUBLE CIRCULATION THROUGH THE HEART RESULTS IN A MUCH HIGHER BLOOD PRESSURE IN THE ARTERIES GOING TO THE BODY.