Reptiles generally have three-chambered hearts consisting of two atria and one partially divided ventricle, allowing some mixing of oxygenated and deoxygenated blood. Crocodiles are an exception with four-chambered hearts like mammals. Reptile cardiovascular physiology differs significantly from mammals in being less affected by changes in oxygen, pH, and heart rate/blood pressure. The heart's location varies between species but is usually within the thoracic cavity or farther back for some lizards and snakes.

2. REPTALIA HEART
CIRCULATORY SYSTEM
Dr. G.D. HANDE

3. •Reptilian hearts differ significantly from those of
mammals.
• Most reptiles possess three chambered hearts, with
the exception of crocodilians.
•The anatomy of the great vessels is quite different
from that of mammals and can be confusing to
uninitiated.
• Adequate knowledge of normal anatomy and
function is paramount in assessing health and
performing certain clinical procedures.

4. Reptile cardiovascular physiology is also
significantly different from that of mammals.
 Reptiles are much less susceptible to the
adverse effects of hypoxia and changes in blood
pH, and therefore capable of enduring much
wider fluctuations in heart rate, blood pressure,
and oxygenation.

5. •Most reptiles have three chambered hearts
with two atria and one common ventricle.
• The right atrium receives blood returning
from the systemic circulation via the sinus
venosus, which is formed by the confluence
of the right and left precaval veins and the
single postcaval vein.

6. The reptilian heart has a partial septum
between the ventricles.
This allows better separation of oxygenated
and deoxygenated blood.
 The separation increases the efficiency of
transporting oxygenated blood to the body.

7. Reptiles have a three-chambered heart –
•Two atria and one partially divided ventricle.
•There is a mixing of oxygenated and
deoxygenated blood because the ventricle is
not split completely.
• The crocodile has a four-chambered
heart similar to mammals and birds where the
ventricles are split completely.

8. Anatomy and function
•The location of the heart within the body
cavity varies according to species.
• In most chelonians the heart lies on midline
just caudal to the thoracic girdle, ventral to the
lungs.
• The heart of some chelonians such as soft-
shelled turtles is pushed to the side of the
body cavity in order to accommodate the
retracted neck.

10. The heart of most lizards lies within the thoracic girdle,
with the exception of some species such as monitors and
crocodilians in which the heart lies farther back in the
coelomic cavity.
 Cardiac location varies in snakes according to species,
but usually is found at the junction of the first and
second quarter of the animal's body length.
Typically arboreal snakes' hearts are found more
cranially in the body than in terrestrial animals.
 Snake's hearts are fairly mobile within the coelomic
cavity helping to facilitate the ingestion of large prey
items.

13. The cardiac structure of reptiles is significantly different
from that of mammals. Please note that the following
descriptions are very general, and that significant variation
exists between species. Most reptiles have three
chambered hearts with two atria and one common
ventricle. The right atrium receives blood returning from
the systemic circulation via the sinus venosus, which is
formed by the confluence of the right and left precaval
veins and the single postcaval vein.

14. •The walls of the sinus venosus contain cardiac muscle
and the pacemaker of the heart. The left atrium
receives oxygenated blood from the lungs via the
pulmonary vein(s).
• The atrioventricular valves are bicuspid,
membranous structures.
• Under normal conditions the three chambered heart
functions much like a four chambered structure,
therefore relatively little mixing of oxygenated and de-
oxygenated blood occurs.

15. •The cardiac structure of reptiles is significantly
different from that of mammals.
•Please note that the following descriptions are very
general, and that significant variation exists between
species.
• Most reptiles have three chambered hearts with two
atria and one common ventricle.
•The right atrium receives blood returning from the
systemic circulation via the sinus venosus, which is
formed by the confluence of the right and left precaval
veins and the single postcaval vein.

16. •The walls of the sinus venosus contain cardiac muscle and
the pacemaker of the heart.
•The left atrium receives oxygenated blood from the lungs
via the pulmonary vein(s).
•The atrioventricular valves are bicuspid, membranous
structures.
•Under normal conditions the three chambered heart
functions much like a four chambered structure, therefore
relatively little mixing of oxygenated and de-oxygenated
blood occurs.

17. •Crocodilians are the only reptiles which possess four
chambered hearts comparable to mammals.
•Even so, crocodilian cardiac anatomy is quite different
from what is seen in birds and mammals.
• Crocodilians possess two aortas; the right arising from
the left ventricle and the left from the right ventricle.
Both aortas route blood to the systemic circulation.