Changes

Oxygenated blood enters the heart in the left atrium and deoxygenated blood enters in the right. The atria contract shortly after one another. Thus part of the heart is filled with oxygenated blood, the greater part with mixed blood and the other part with deoxygenated blood.  During the ventricular systole, the blood is directed into the large arteries, at the base of the heart, so that oxygenated blood is directed to the brain; mixed blood is directed to the body and deoxygenated blood to the lungs. The atrioventricular valve prevents backflow of blood from the heart and three semilunar valves prevent this from the arteries to the heart.   

Oxygenated blood enters the heart in the left atrium and deoxygenated blood enters in the right. The atria contract shortly after one another. Thus part of the heart is filled with oxygenated blood, the greater part with mixed blood and the other part with deoxygenated blood.  During the ventricular systole, the blood is directed into the large arteries, at the base of the heart, so that oxygenated blood is directed to the brain; mixed blood is directed to the body and deoxygenated blood to the lungs. The atrioventricular valve prevents backflow of blood from the heart and three semilunar valves prevent this from the arteries to the heart.   

* During normal respiration, the flow of blood tends to create a left to right shunt based upon pressure differentials. This is the recirculation through the pulmonary circulation of oxygenated blood.

* During normal [[Lizard and Snake Respiration|respiration]], the flow of blood tends to create a left to right shunt based upon pressure differentials. This is the recirculation through the pulmonary circulation of oxygenated blood.

* During diving or other instances in which the pulmonary resistance and pressure are elevated, a right to left shunt occurs. It represents the recirculation of systemic blood through the systemic arterial circulation. Pulmonary bypass means the blood is not re-oxygenated.

* During diving or other instances in which the pulmonary resistance and pressure are elevated, a right to left shunt occurs. It represents the recirculation of systemic blood through the systemic arterial circulation. Pulmonary bypass means the blood is not re-oxygenated.