Human Heart Diagram Labeled

The human heart is an organ responsible for pumping blood through the body, moving the blood (which carries valuable oxygen) to all the tissues in the body. Without the heart, the tissues couldn’t get the oxygen they need and would die. Along with lymphatic vessels, the blood, blood vessels, and lymph, the heart composes the circulatory system of the body.

Let’s examine the anatomy of the heart along with some diagrams that show how the heart operates.

Anatomy Of The Heart

The human heart usually weighs somewhere between 10 to 12 ounces in men and between 8 to 10 ounces in women, and in terms of size is roughly the size of the fist. The heart has four different chambers: the left and right ventricles and the left and right atriums. The chambers of the heart and the valves that regulate blood flow to them are considered the plumbing of the heart. The left ventricle and left atrium make up the left heart while the right ventricle and right atrium make up the right heart. While there are four different chambers of the heart, the chambers work together and the heart basically functions as a single organ. The muscle tissue dividing the two halves of the heart is referred to as the septum.

Location of valves in the heart. Photo: By OpenStax College – Anatomy & Physiology, Connexions Web site., Jun 19, 2013., CC BY 3.0,

Four different valves are responsible for controlling how blood moves through the heart. If blood were to start flowing in the wrong direction (ex. out of the heart from an area that should be receiving blood from the rest of the body), it is referred to as backflow or regurgitation. If this backflow or regurgitation is severe enough, the heart will not be able to meet the need for blood in all regions of the body, and difficulty breathing or other harmful and painful symptoms may occur. The valves of the heart are there to ensure that blood only flows in one direction, minimizing the chance for backflow. The tricuspid valve controls blood flow for the right ventricle and right atrium. The aortic valve lets oxygen-enriched blood come to the aorta from the left ventricle, while the mitral valve facilitates the movement of oxygenated blood to the left ventricle, coming from the left atrium.

Blood is pumped through the four chambers of the heart by a series of rhythmic contractions. These contractions are controlled by electrical impulses. The electrical impulses originate from a structure found at the top of the heart’s right atrium, the sinoatrial node. This note sends electrical impulses to the muscles of the heart, and when the myocardium receives the signals, they contract. The electrical signals are sent out at a constant, rhythmic rate. However, one’s heart rate can be affected by things such as physical stress, mental stress, and hormonal factors.

The pericardium is a structure that encases the heart, a sturdy structure made out of a double wall of tissue. The function of the pericardium is to hold the heart in a permanent place within the chest and give the heart protection. The outer layer of the pericardium is referred to as the parietal pericardium, and the serous pericardium is the inner layer of the structure. The myocardium is the middle portion of the outer wall, and these muscles are what causes the contraction of the heart, contracting upon reception of electrical impulses from the sinoatrial node. The endocardium is the inner portion of the outer wall, and the endocardium is what contacts the blood in the heart.

The heart’s atrioventricular valves are structures that join the atria and ventricles of the heart together. This group of valves is comprised of the tricuspid valve and the mitral valve. Beyond this, there is a structure referred to as the aortic valve which separates the left ventricle and the aorta. In a similar fashion, the pulmonary semilunar valve functions to keep the right ventricle and pulmonary artery separate from one another. The muscles of the heart hold onto the valves thanks to heartstrings or the chordae tendinae.

Pumping Blood Through The Body

The circulatory system surrounding the heart. Photo: By Blausen Medical Communications, Inc. – Donated via OTRS, see ticket for details, CC BY 3.0,

The heart’s primary function is to supply the tissues of the body with oxygen and rid the body of carbon dioxide. The pulmonary circuit and the systemic circuit are the two systems of the body that enable the heart to accomplish this.

Deoxygenated blood is oxygenated as leaves through the pulmonary circuit. The pulmonary artery takes the blood which leaves the right ventricle of the heart, deoxygenated at this point, and transports the blood to the lungs. In the lungs, the deoxygenated blood picks up oxygen. This newly oxygenated blood will go back to the heart by way of the pulmonary vein and left atrium. By contrast, the systemic circuit transports oxygenated blood to the rest of the body. The arteries and capillaries of the body deliver the oxygenated blood to the various tissues in the body, giving them the oxygen they need to function. After the oxygen has been supplied into the tissues, the deoxygenated blood uses the veins of the body to enter the right atrium of the heart via the venae cavae.

Every group of tissue in the body needs oxygen to function, and this includes the heart. Since the heart needs oxygen as well, how does it supply itself with oxygen? The heart receives oxygen when the blood is passing out of the heart through the aortic valve. There are two different arteries which are responsible for transporting some blood to the heart. The coronary artery and the circumflex artery are responsible for delivering oxygenated blood to the heart and break up into several branches in the heart region.

A cardiac arrest or heart attack can occur if the arteries that supply the heart with blood are blocked. Heart attacks can potentially be different from cardiac arrest, though there is some overlap between the two conditions. Cardiac arrest occurs when the heart ceases to function properly, and while various conditions can lead to cardiac arrest, the primary cause of cardiac arrest is the upset of the heart’s regular rhythm. A heart attack can interrupt the rhythm at which the heart beats, but it isn’t the only way for cardiac arrest to occur. The heart has its own cells that ensure contractions happen at the proper rhythm, natural pacemaker cells. Each one of these pacemaker cells can follow a certain rhythm or set the rhythm for the heart to beat at. Irregular heartbeat and atrial fibrillation problems can occur when the various pacemaker cells within the heart are trying to establish their own rhythms, and as a result, the cells will beat out of sync instead of in rhythm.

Regular healthy heart contractions are carried out in different phases. The first phase of a heart contraction is early diastole. In this phase the heart is relaxed. The second phase of the contraction is when the atrium of the heart pushes the blood into the ventricles, and this phase is referred to as atrial systole. The ventricles begin contracting during the third phase of the process, ventricular systole. The volume of the ventricle doesn’t change during ventricular systole. The fourth phase of the process is atrial diastole, and during this phase, the atria is filled with blood coming from the vena cavae. Finally, the last phase of the contraction process is referred to as ventricular diastole, and it is where the ventricles fill with blood coming from the atria. This phase actually starts slightly before atrial diastole, though it may finish afterward.

List Of Heart Structures

Heart Chambers

  • Ventricles – The bottom two heart chambers.
  • Atra – The upper two heart chambers.

Wall Of The Heart

  • Sinoatrial Node – A collection of tissue that releases electrical impulses and defines the rate of contraction for the heart.
  • Atrioventricular Bundle – The fibers which transmit cardiac impulses.
  • Atrioventricular Node – Nodal tissue which relays cardiac impulses and assists the sinoatrial node in causing contractions.

Valves Of The Heart

  • Mitral Valve – Functions to prevent backflow of blood during the pumping of blood into the left ventricle from the left atrium.
  • Aortic Valve – Functions to prevent the backflow of blood while it is pumped to the aorta from the left ventricle of the heart.
  • Tricuspid Valve – Prevents the reversal of blood flow while the blood is pumped into the right ventricle from the right atrium.
  • Pulmonary Valve – Prevents the reversal of blood flow while the blood is pumped into the pulmonary artery from the right ventricle.


  • Aorta – The aorta is the structure from which the majority of the major arteries branch off from. It is also the biggest artery in the human body.
  • Brachiocephalic Artery – This artery is responsible for transporting blood from the aorta to the arms, neck, and head.
  • Carotid Arteries – These arteries bring blood to the neck and head from the heart.
  • Common iliac arteries – These arteries transport blood from the heart to the legs and feet, originating at the abdominal aorta.
  • Coronary arteries – The coronary arteries transport blood to the heart itself.
  • Pulmonary artery – This artery brings deoxygenated blood to the lungs from the heart’s right ventricle.
  • Subclavian Arteries – The subclavian arteries transport blood to the arms.


  • Pulmonary Veins – These veins are what transport blood and oxygen to the heart from the lungs.
  • Venae Cavae – These are responsible for transporting de-oxygenated blood to the heart from the other parts of the body.
  • Common iliac veins – These veins join together to compose the inferior venae cavae.
  • Brachiocephalic veins – The brachiocephalic veins join together to compose the superior venae cavae.