The snake, like other reptiles, has a three-chambered heart, consisting of one ventricle and two atria. In this case, the ventricle is divided into two halves by the septum: the upper and lower. After atrial contraction, arterial blood from the left atrium is in the upper half of the ventricle and displaces the venous blood poured from the right side of the ventricle into the lower half. In the right part of the ventricle is mixed blood.
When the ventricle contracts, the blood rushes to the nearest hole: the arterial blood from the upper half – into the right arch of the aorta, the venous blood from the lower half into the pulmonary artery, and the mixed blood from the right side of the ventricle into the left arch of the aorta.
Since the right aortic arch carries blood to the brain, the brain receives the most oxygen-enriched blood.
Reptiles have three independent vessels: the pulmonary artery, and the right and left arcs of the aorta. Each aortic arch bends back around the esophagus, and, converging with each other, they unite into an unpaired dorsal aorta.
In the boa and python, the arteries of the heart are clearly distributed on the right and left coronary arteries, both of which supply blood to the ventral and dorsal surfaces of the ventricle. The main trunks of the arteries are located in the atrioventricular sulcus and can be called coronary, as they round the heart from two sides.