Your heart is a muscular organ, about the size of your fist, that works tirelessly to pump blood throughout your body. Think of it as a duplex house with four rooms, or chambers. The two upper chambers are called the atria (singular: atrium), and the two lower chambers are the ventricles.

The right side of the heart handles deoxygenated blood. Blood from your body enters the right atrium, which then pushes it down into the right ventricle. The right ventricle's job is to pump this blood to the lungs to pick up oxygen.

Once the blood is oxygenated, it returns to the left side of the heart, entering the left atrium. The left atrium sends this fresh, oxygen-rich blood into the powerful left ventricle. The left ventricle is the strongest chamber, as it needs to pump blood out to the entire rest of your body through a large artery called the aorta.