Lernizy
Biology

The Human Heart: Structure, Function & Blood Circulation

Your body's tireless pump

The human heart is a muscular organ about the size of your fist, located slightly left of center in your chest. It beats roughly 100,000 times every day, pumping around 7,500 liters of blood through a network of vessels that would stretch over 96,000 kilometers if laid end to end. This double-pump system keeps oxygen-rich blood flowing to every cell while sending oxygen-poor blood to the lungs for renewal.

Anatomical cross-section diagram of the human heart showing four chambers, major blood vessels, valves, and the directional flow of blood through pulmonary and systemic circulation pathways

Tap the + pins to see what each part is called

Key Features

Four-chambered design

Two upper atria receive blood while two lower ventricles pump it out, creating separate pathways for oxygen-rich and oxygen-poor blood that never mix.

Electrical conduction system

The sinoatrial node (SA node) acts as a natural pacemaker, sending electrical signals that coordinate each heartbeat without any conscious control from your brain.

One-way valve system

Four valves (tricuspid, pulmonary, mitral, bicuspid) open and close in precise sequence to prevent backflow, creating the familiar 'lub-dub' sound of a heartbeat.

Double circulation

Pulmonary circulation carries blood to the lungs for oxygen, while systemic circulation delivers that oxygenated blood to the rest of the body through a single pump.

Cardiac muscle tissue

Unlike skeletal muscle, cardiac muscle never fatigues. Its cells are branched and interconnected, allowing the entire heart wall to contract as one coordinated unit.

Breakdown

Right atrium
Receives deoxygenated blood from the body through the superior and inferior vena cava.
Right ventricle
Pumps deoxygenated blood to the lungs through the pulmonary artery for gas exchange.
Left atrium
Receives oxygen-rich blood returning from the lungs via four pulmonary veins.
Left ventricle
The thickest chamber, pumps oxygenated blood through the aorta to the entire body with enough force to reach your toes.
Septum
The muscular wall dividing the heart into left and right halves, preventing any mixing of oxygenated and deoxygenated blood.
Coronary arteries
Branch off from the aorta to supply the heart muscle itself with oxygen and nutrients.
Pericardium
A double-layered protective sac surrounding the heart, containing lubricating fluid that reduces friction during contractions.

Did you know?

  • • Your heart pumps blood through three types of blood vessels: arteries (carry blood away), veins (carry blood back), and capillaries (exchange nutrients and waste).
  • • A woman's heart typically beats 8 beats per minute faster than a man's heart at rest.
  • • The left lung is smaller than the right lung specifically to make room for the heart.
  • • Laughing is good for your heart because it causes blood vessels to dilate by 22%, increasing blood flow temporarily.
Written by Lernizy Editorial Team
Updated 25 Jul 2026