TracheaC-shaped pieces of cartilage, stacked one above the other, form the tube.
Primary bronchiThe trachea branches into right and left primary bronchi at the carina. Each bronchus enters its lung at the hilum.
Right lungIt is shorter and wider than the left lung. It has three lobes.
Left lungIt takes up a smaller volume than the right lung. It has two lobes.
Cardiac notchAn indentation on the surface of the left lung. It allows space for the heart.
HeartIt lies in the chest between the lungs. It is broad at the top, where the great vessels join it, and tapers to a point called the apex.
PericardiumAlso called the pericardial sac. It separates the heart from the other structures in the middle of the chest.
MediastinumThe heart and its great vessels lie in it. So do the trachea and the esophagus.
Superior vena cavaIt drains blood from the head, neck, upper limbs and chest. It empties into the right atrium.
AortaThe largest artery in the body. It arises from the left ventricle; three branches leave the top of its arch.
DiaphragmA dome-shaped muscle at the base of the lungs and chest cavity.
The pulmonary circuit 8
Right ventricleIt pumps blood that is low in oxygen into the pulmonary trunk.
Pulmonary trunkIt divides into the right and left pulmonary arteries. Also called the main pulmonary artery.
Right pulmonary arteryIt branches again and again inside the lung, down to pulmonary capillaries.
Left pulmonary arteryThe pulmonary trunk and its arteries carry blood low in oxygen. No other arteries do after birth.
Pulmonary capillariesGas exchange happens here. Carbon dioxide leaves the blood and oxygen enters it.
AlveoliThe pulmonary capillaries surround them. Oxygen and carbon dioxide are exchanged across their walls.
Pulmonary veinsThere are four, two from each lung. They return blood that is rich in oxygen to the left atrium.
Left atriumIt receives blood from the pulmonary veins. It passes that blood to the left ventricle, which pumps it into the aorta.
How this list was compiled: Every name and detail checked on 2026-09-30 against OpenStax Anatomy and Physiology 2e, sections 19.1 Heart Anatomy (position of the heart, mediastinum, pericardium, great vessels, superior vena cava), https://openstax.org/books/anatomy-and-physiology-2e/pages/19-1-heart-anatomy, 20.5 Circulatory Pathways (the pulmonary circuit, the aorta), https://openstax.org/books/anatomy-and-physiology-2e/pages/20-5-circulatory-pathways, 22.1 Organs and Structures of the Respiratory System (trachea, primary bronchi, alveoli), https://openstax.org/books/anatomy-and-physiology-2e/pages/22-1-organs-and-structures-of-the-respiratory-system, and 22.2 The Lungs (the two lungs, cardiac notch, diaphragm), https://openstax.org/books/anatomy-and-physiology-2e/pages/22-2-the-lungs, and against Wikipedia, Pulmonary circulation, Pulmonary artery, Lung, Heart and Mediastinum, text only. Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Licence: own work
How it works
This diagram of the lungs and heart has two drawings. The first is the chest from the front, with the heart between the lungs. The second is a plan of pulmonary circulation: right ventricle, lungs, left atrium.
Read the full guide
Start in the chest
Numbers 1 to 11 are the chest from the front. The person faces you, so the right lung is on the left of the drawing. The heart sits between the lungs, and the left lung has a notch that makes room for it.
Then follow the blood
Numbers 12 to 19 follow the pulmonary circuit in order: out of the right ventricle, up the pulmonary trunk, along an artery into each lung, through the capillaries round the alveoli, and back along the pulmonary veins to the left atrium. The arrows show the way.
Arteries carry blood away from the heart and veins carry it back. In this circuit the arteries carry the blood that is low in oxygen.
Questions and answers
How are the heart and lungs connected?
By the pulmonary circuit. The pulmonary trunk leaves the right ventricle and divides into a right and a left pulmonary artery, one to each lung. Four pulmonary veins, two from each lung, carry the blood back to the left atrium.
Where is the heart in relation to the lungs?
Between them. The heart lies in the mediastinum, the middle part of the chest, inside a tough sac called the pericardium. The left lung has an indentation, the cardiac notch, that allows space for the heart.
What happens to blood in the lungs?
In the pulmonary capillaries, which surround the alveoli, carbon dioxide leaves the blood and oxygen enters it. The blood then returns to the heart through the pulmonary veins.
Why do the pulmonary arteries carry blood low in oxygen?
An artery is a vessel that carries blood away from the heart. The pulmonary trunk and its arteries take blood from the right ventricle to the lungs, before it has picked up oxygen there.
Which lung is bigger, the right or the left?
The right lung is shorter and wider than the left, and the left lung takes up a smaller volume. The right lung has three lobes and the left lung has two.