Anatomy of the human heart

A newborn baby has about one cup of blood in circulation. An adult human has about four to five quarts which the heart pumps to all the tissues and to and from the lungs in about one minute

Your heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone (sternum). A double-layered membrane called the pericardium surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your heart's major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body. The inner layer of the pericardium is attached to the heart muscle. A coating of fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to your body. Your heart has 4 chambers. The upper chambers are called the left and right atria, and the lower chambers are called the left and right ventricles. A wall of muscle called the septum separates the left and right atria and the left and right ventricles. The left ventricle is the largest and strongest chamber in your heart. The left ventricle's chamber walls are only about a half-inch thick, but they have enough force to push blood through the aortic valve and into your body.

The coronary arteries supply oxygenated and nutrient filled blood to the myocardium itself

Coronary Arteries: Branches

Some of the arteries that extend from the main coronary arteries include:
  • Right Coronary Artery - Supplies oxygenated blood to the walls of the ventricles and the right atrium.
    • Posterior Descending Artery - Supplies oxygenated blood to the inferior wall of the left ventricle and the inferior portion of the septum.
  • Left Main Coronary Artery - Directs oxygenated blood to the left anterior descending artery and the left circumflex. 
    • Left Anterior Descending Artery - Supplies to the anterior portion of the septum as well as to the walls of the ventricles and the left atrium (front region of the heart). 
    • Left Circumflex Artery - Supplies oxygenated blood to the walls of the ventricles and the left atrium (back region of the heart).

The Heart Valves

Four types of valves regulate blood flow through your heart:

  • The tricuspid valve regulates blood flow between the right atrium and right ventricle.
  • The pulmonary valve controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to your lungs to pick up oxygen.
  • The mitral valve lets oxygen-rich blood from your lungs pass from the left atrium into the left ventricle.
  • The aortic valve opens the way for oxygen-rich blood to pass from the left ventricle into the aorta, your body's largest artery, where it is delivered to the rest of your body.

An average human heart weighs around 250-300g in females and 300-350g in males.

The Conduction System

Electrical impulses from your heart muscle (the myocardium) cause your heart to contract. This electrical signal begins in the sinoatrial (SA) node, located at the top of the right atrium. The SA node is sometimes called the heart's "natural pacemaker." An electrical impulse from this natural pacemaker travels through the muscle fibers of the atria and ventricles, causing them to contract. Although the SA node sends electrical impulses at a certain rate, your heart rate may still change depending on physical demands, stress, or hormonal factors.

Physician Erasistratus of Chios (304-250 B.C.) was the first to discover that the heart functioned as a natural pump.