Take a look inside a model of a heart. There are four cavities, or open spaces, inside the heart that fill with blood. Two are called atria (one is called an atrium), and the other two are called ventricles. A wall, called the septum, separates the right and left sides of the heart. A valve connects top and bottom cavities on each side. This is called the Coronary Circulation System.

Do left and right seem a little mixed up to you here? Imagine that you are looking at the heart of a person who is facing you. It would be their right and left that match the right and left of the heart in the diagram.

Quick Menu: Cardio | Intro | Heart | Lungs | Activity 1 | Blood Vessels | Activity 2