Your heart works nonstop to deliver nutrient-rich blood to every part of the body, but its first priority is always to take car­e of No.

1 -- itself. You can think of it like this: When you deposit money into a checking account, you establish a system where all of your money passes from you to your bank and then follows one of two paths. It may either earn interest while the bank loans it out, or it may scatter to pay your various expenses.
Before that money scatters, the bank earmarks some of those funds for itself first. When you look at your statement, you can see all of the deductions from your account, and there at the top is the monthly checking account fee. Your heart handles blood in much the same way.
The heart pumps about 2,000 gallons (7,571 liters) of blood a day through its chambers. Of ­course, we're not big enough to hold that much liquid, so it just pumps the same blood over and over, and it doesn't benefit from a drop of it.