Right atriumThe upper chamber on the dog's right. Blood from the body enters it through the two venae cavae.
Right ventricleThe lower chamber on the right. It pumps blood through the pulmonary valve to the lungs.
Left atriumThe upper chamber on the left. Blood comes back to it from the lungs through the pulmonary veins.
Left ventricleThe lower chamber on the left. It pumps blood via the aortic valve to the aorta and on to the whole body.
Tricuspid valveThe inlet valve of the right ventricle. In the dog it has two main flaps and three or four small ones. Anatomists also call it the right atrioventricular valve.
Mitral valveThe inlet valve of the left ventricle. It has two large flaps. Also called the bicuspid or left atrioventricular valve.
Pulmonary valveThe outlet valve of the right ventricle, with three pocket-shaped flaps. It opens into the pulmonary trunk.
Aortic valveThe outlet valve of the left ventricle, with three pocket-shaped flaps. It opens into the aorta.
Cranial vena cavaThe large vein from the head, neck and fore legs. It brings their blood to the right atrium. Older books call it the anterior vena cava.
Caudal vena cavaThe large vein from the rear of the body. It brings blood to the right atrium. Older books call it the posterior vena cava.
Pulmonary trunkThe artery that leaves the right ventricle. It splits into the right and left pulmonary arteries, one to each lung.
Pulmonary veinsThe veins that bring blood from the lungs to the left atrium. A dog usually has six.
AortaThe largest artery of the body. It rises from the left ventricle and arches back toward the spine.
The heart in the chest 12
BaseThe wide end of the heart, where the great vessels join it. In the dog it faces forward, toward the front opening of the chest, level with the third rib.
ApexThe blunt, rounded tip of the heart. It points down and back and lies on the left side at about the seventh rib, close to the diaphragm.
RibsA dog has thirteen pairs. They are cut short here to show the chest; the heart lies under the third to the seventh.
SternumThe breastbone: a row of eight pieces along the chest floor. The heart rests on its rear half.
DiaphragmThe sheet of muscle between the chest and the abdomen. The apex of the heart lies close against its lower part.
Left lungThe lungs fill the chest on both sides of the heart. The left lung has two lobes, a cranial one and a caudal one.
TracheaThe windpipe. It divides into two principal bronchi, one for each lung.
Aortic archThe bend of the aorta as it leaves the heart. Here it turns back toward the spine. Two arteries leave the arch.
Brachiocephalic trunkThe first and larger branch of the arch. Both carotid arteries, to the head, and the right subclavian artery, to the right fore leg, come from it.
Left subclavian arteryThe second branch of the arch. It leaves the chest at the first rib to supply the left fore leg. Older books call it the left brachial artery.
Descending aortaThe aorta after the arch, running back under the spine. In the chest it is also called the thoracic aorta.
Phrenicopericardial ligamentA band that ties the sac round the heart to the diaphragm. In the dog the sac is joined to the diaphragm in this way, and not to the sternum.
How this list was compiled: Every name checked on 2026-09-30 in two sources. S. Sisson, The Anatomy of the Domestic Animals (1914, public domain), the dog: the shape and position of the heart against the ribs, sternum and diaphragm, its ligament, valves, veins and great vessels, https://archive.org/details/anatomyofdomesti00siss. Merck Veterinary Manual, dog owner version, for the four chambers, four valves, the path of the blood and the resting heart rate, https://www.merckvetmanual.com/dog-owners/heart-and-blood-vessel-disorders-of-dogs/introduction-to-heart-and-blood-vessel-disorders-in-dogs. University of Minnesota College of Veterinary Medicine, Carnivore Anatomy Labs 10 to 12, for today's veterinary names of the vessels, valves, lung lobes and the ligament, http://vanat.cvm.umn.edu/carnLabs/Lab12/Lab12.html. 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 dog heart diagram has two views. The first opens the heart to show its four chambers, four valves and great vessels. The second shows where the heart sits in the chest of a standing dog. It is a plan, not to scale.
Read the full guide
Inside the heart
In this diagram of a dog's heart the dog's right side is at the left of the picture. Blood from the body enters the right atrium, passes to the right ventricle and goes to the lungs. It returns to the left atrium, passes to the left ventricle and leaves by the aorta.
In the chest
Switch to In the chest for a dog heart location diagram. The heart is egg-shaped and set at a slant: its base faces forward at the third rib, and its apex rests low on the left near the seventh rib and the diaphragm. Press Quiz me to name each part yourself.
Vets say cranial and caudal vena cava. Books on the human body say superior and inferior. They are the same two veins.
Questions and answers
Where is a dog's heart located?
In the chest, between the lungs, low down and mostly toward the left. Its base is level with the third rib. Its tip, the apex, is at about the seventh rib, close to the breastbone and the diaphragm.
How many chambers does a dog's heart have?
Four, as in all mammals and birds: a right and a left atrium above, and a right and a left ventricle below.
How big is a dog's heart?
About 1 percent of the dog's body weight, by a standard veterinary anatomy text. The share is larger in hunting dogs and dogs worked for speed.
How fast does a dog's heart beat?
At rest, about 60 to 120 times a minute. Larger animals have slower hearts: a horse's beats about 30 times a minute, and a cat's more than 120.