Describe the external structure of the human heart.

(N/A) The human heart is a mesodermally derived organ.
It is situated in the thoracic cavity,in between the two lungs,and is slightly tilted to the left.
It is approximately the size of a clenched fist.
It is protected by a double-walled membranous bag called the pericardium,which encloses the pericardial fluid.
The human heart has four chambers: two relatively small upper chambers called atria and two larger lower chambers called ventricles.
Although the ventricles are larger than the atria,they contain the same volume of blood.
The atria and ventricles are separated externally by a clear groove known as the coronary sulcus or cardiac septum.
The ventricles are separated by the interventricular septum,which contains coronary arteries that supply oxygenated blood to the heart muscle itself.