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.