F rom the title of this article , you may surmise that it is about the cold-hearted nature of crocs , renowned for their ferocity as man-eaters . Or perhaps , for those who are more informed about crocodile behaviour , you may be expecting something about the tender-heartedness of mother crocodiles , who carry their tiny newly-hatched babies ever so gently in their strong jaws , as well as defending them , communicating to them and teaching them as they grow . Well , that will have to wait for another time . The title of this article is no metaphor , as it concerns the physical heart of a crocodile : its structure and function . For crocodilians ’ ( crocodiles , alligators and gharials ) hearts are complex and unique , allowing them to be both very active predators when required , and also to save energy when resting or submerged underwater .
Most reptiles have three-chambered hearts : a left and right atrium , and a single , partially-divided ventricle . This contrasts with mammals ( including humans ) and birds , which have a fourchambered heart . In the latter , deoxygenated blood , returning from being pumped around the body , enters the right atrium , flows into the right ventricle , and is pumped out through the pulmonary artery to the lungs where it picks up oxygen . The newly-oxygenated blood then returns to the heart via the pulmonary vein , entering the left atrium , and then flowing into the left ventricle . This most muscular chamber of the heart then pumps the blood out through the aorta , to flow around the body and provide tissues with the oxygen required for metabolic activity . The complete separation of all the chambers ( and therefore also pulmonary and systemic circulatory systems ) means there is no mixing of deoxygenated and oxygenated blood , ensuring that blood leaving the left side of the heart is maximally oxygenated . In contrast , because the ventricle of lizards is not completely divided into left and right chambers , some mixing of blood occurs . This isn ’ t too much of an issue for these ectothermic animals , but does limit their maximum aerobic capacity . Mammals and birds have a higher demand for oxygen , as they must fuel their constant high metabolic rate in order to regulate body temperature endothermically . Crocodiles also possess a four-chambered heart , but it is something of a hybrid , and unlike that of any mammal !
Now crocodiles can be very fast when they need to be , and part of this is thanks to the separation of oxygenated from deoxygenated blood . But they also spend long periods underwater , waiting for unsuspecting prey . When submerged , a premium is placed on conserving oxygen , since obviously they cannot breathe and replenish their oxygen supply underwater . The unique arrangement of their heart means that they can be more flexible in their patterns of blood circulation than either mammals or birds ( which are in fact more closely related , evolutionarily speaking , to crocodiles than lizards are ).
Firstly , crocodiles have two aortas ( the primary blood vessel that carries oxygenated blood away from the heart ), rather than a single one arising from the left ventricle as in mammals and birds . Other reptiles also have two aortas , however in crocodiles they arise from different ventricles – perplexingly , the left aorta emerges from the right ventricle , adjacent to the pulmonary artery , whereas the right aorta arises from the left ventricle . Both have a bicuspid valve at the base which regulates the flow of blood . Crocodiles ’ aortas also differ from other reptiles in that they are highly asymmetric : with the right aorta being considerably larger than the left . This is matched by blood flow , with the right aorta carrying most of the oxygen-rich blood that flows from the heart .
When the crocodilian is not submerged , and able to breathe air , the right aorta receives oxygenated blood from the left ventricle , which is pumped around the body . The left aorta is usually closed by a valve where it leaves the right ventricle . This prevents blood which is low in oxygen from being sent out to respiring tissues ; rather it is directed to the lungs via the pulmonary circuit , which also arises out of the right ventricle . Instead , the left aorta receives oxygenated blood from the right aorta during diastole through an opening connecting the two vessels , called the foramen of Panizza ( after Bartolomeo Panizza , the anatomist who , in 1833 , published the first paper on the complexity of the crocodilian cardiovascular anatomy ). The foramen of Panizza is unique to crocodiles , and contributes to the functional complexities of their cardiovascular system .
When a crocodile is submerged underwater , a different circulatory pattern occurs . There is little point in pumping blood through the lungs , as this is a waste of energy . It is far more adaptive to