(Choose the best main idea)
The heart is the most vital organ of human being.
The heart is a muscular organ that pumps blood throughout the body delivering oxygen and trans forming carbon dioxide.
Blood with oxygen is pumped away from the heart through blood vessels called arteries.
After travelling through the body the blood then circulates back to the heart carrying carbon dioxide in other blood vessels called veins.
Inside the heart the carbon dioxide is taken out of the blood and and oxygen is returned.