Medical Learning Library

Anatomy of the Heart

The human heart is a muscular organ—about the size of an adult fist—located slightly left, anterior of the vertebral column, and posterior of the sternum. It is responsible for pumping oxygenated blood to the body and deoxygenated blood to the lungs through continuous rhythmic contractions.

Heart Location.BruceBlaus/Wikimedia Commons/CC-BY-SA-3.0)

How the Heart Beats

The myogenic heartbeat originates from the sinoatrial (SA) node—a natural, intrinsic pacemaker—within the heart itself rather than from specific nerve impulses.

Without extrinsic neural (autonomic nervous system) or hormonal influences (endocrine system) the SA node pacing rate would be around 100 beats per minute.

The heart rate and cardiac output, however, must alter under varying circumstances in response to the demands of the body for oxygen and nutrients. The nervous system, hormones, and other factors influence this action.

The average heart rate changes through the lifespan:

Your Heart’s Electrical System

Autonomic and Endocrine Control of Cardiovascular Function

Heart Contraction: Diastole and Systole

How the Heart Works

Kids Health: Your Heart and Circulatory System

The Science Behind Compressions

Layers of the Heart Wall


Heart Valves.OpenStax College/Wikimedia Commons/CC-BY-SA-3.0)

A double-membrane sac, the pericardium, encloses three layers of the heart.

Diagnosis and Management of Pericardial Effusion

Exterior of the Heart


Diagram of the Heart.Wapcaplet/Wikimedia Commons/CC-BY-SA-3.0/GFDL)

Several main blood vessels of the circulatory system connect to the heart by its exterior to supply blood to the heart itself (coronary circulation) and to the four chambers inside the heart (left atria, right atria, left ventricle, and right ventricle).

The right atrium receives deoxygenated blood from the inferior vena cava and superior vena cava and then sends it to the right ventricle.

The right ventricle contracts to pump the deoxygenated blood from the heart to the lungs, via the pulmonary arteries, to expel carbon dioxide during exhalation and pick up oxygen during inhalation.

From the lungs, through the pulmonary veins, the left atrium receives the oxygen-rich blood and pumps it into the left ventricle.

The left ventricle contracts to deliver the oxygenated blood out the aorta to the cells within the body.

Gas Exchange Health Video

Classification and Structure of Blood Vessels

Accurate Definition of the Widowmaker Heart Attack

Fetal Circulation – The umbilical vein supplies the fetus with oxygen-rich blood from the placenta and the fetal heart pumps oxygen-depleted blood via the umbilical arteries back to the placenta.

Right Side of the Heart

The right side of the heart—the right atrium—is where the largest veins, the inferior vena cava and superior vena cava, return deoxygenated blood from the lower and upper parts of the body.

From these veins, the blood travels into the right atrium and is pumped into the right ventricle.

From the right ventricle, the blood is then pumped through the pulmonary arteries into the lungs.

Reference Ranges For Normal Cardiac Chamber Size

Double Outlet Right Ventricle (DORV)

Left Side of the Heart

The left side of the heart—the left atrium—provides a space to receive oxygen-rich blood from the lungs. The blood travels from the lungs, through the pulmonary veins, and then into the left ventricle.

From the left ventricle, the oxygenated blood is ejected out the aorta to circulate within the rest of the body.

Left Atrium and Pulmonary Veins

Left Atrium Dimensions

Understanding Heart Function: What Is the Ejection Fraction?

Interior of the Heart

The interior of the heart helps maintain the life-sustaining flow of blood. A wall of tissue, known as the septum divides the heart into two halves—this prevents oxygen-rich blood and oxygen-depleted blood from mixing.

During the cardiac cycle, blood passes through valves that act as one-way inlets for blood flowing into a ventricle and one-way outlets for the blood leaving a ventricle. The Four valves of the heart open and close at precisely synchronized times during one heartbeat.


Heart Valves.OpenStax College/Wikimedia Commons/CC-BY-SA-3.0)

Atrial Septal Defect

Ventricular Septal Defect

Most Common Congenital Heart Defect

Cardiovascular Images

How Blood Flows Through the Heart: Video Tutorial

Written by and last updated Sep 3, 2017

Last reviewed by on Oct 11, 2016