The heart is a hollow organ that pumps blood through the cardiovascular system. It is made of a specialized muscle tissue called myocardium. The myocardium requires a consistent flow of blood to work effectively. It is an involuntary muscle and under control of the autonomic nervous system.

There are two main arteries that nourish the heart with blood: the right coronary artery and the left coronary artery. Both descend directly from the aorta. Blockage in these arteries can lead to a reduced flow of blood to the heart. The anterior descending branch of the left coronary artery is a commonly blocked vessel.

The heart has four chambers that contract in coordination to pump blood. The two chambers on top are called the atria. The bottom chambers are called ventricles.

View photos of network of coronary arteries (external link: PBS)

View video of diseased coronary arteries (external link: Science Museum of Minnesota)
[requires Quicktime, click the "play" icon to start]