Cardiovascular system

the heart is a hollow four chambered muscular organ which sits inbetween the lungs. 

the walls are mostly made of cardiac muscle. 

[briefly explain the way de oxygenated blood is turned into oxygenated blood]

the heart has 4 chambers; 

right atrium, left atrium, right ventricle, left ventricle 

cardiac muscles are involantary 

the cardiovascular system includes the heart,blood vessels and blood.

some main functions are; 

transporting oxygen and nutrients

removing waste products 

controlling body temperature

…