Right atriumThe upper chamber on the bird's right. Blood from the body enters it through three large veins.
Left atriumThe upper chamber on the bird's left. Blood comes back to it from the lungs.
Right ventricleThe lower chamber that pumps blood to the lungs. Its wall is thin.
Left ventricleThe lower chamber that pumps blood to the whole body. It makes up most of the cone.
ApexThe pointed end of the heart. In the bird it points toward the tail and a little to the left.
Aortic archThe aorta where it bends over from the heart. In a bird it arches to the bird's right.
Brachiocephalic arteriesTwo large arteries from the aorta, a left and a right. Each sends blood to the head and a wing.
Pulmonary trunkThe artery from the right ventricle. It soon splits in two, one branch to each lung.
The ventricles cut open 7
Right atrioventricular valveA thick flap of muscle between right atrium and right ventricle. It has none of the fine cords of the left valve.
Left atrioventricular valveThin flaps between left atrium and left ventricle. Fine cords hold them from below.
Chordae tendineaeFine cords from the left valve's flaps down to the papillary muscles.
Papillary muscleA mound of muscle on the ventricle wall. The valve's cords are fixed to it.
Interventricular septumThe wall of muscle between the two ventricles. It bulges toward the right one.
Right ventricle wallThe thin outer wall of the right ventricle. The chamber inside it is a narrow, curved space.
Left ventricle wallThe thick outer wall of the left ventricle. It is several times thicker than the right wall.
How this list was compiled: Every name was checked on 2026-10-01 in two sources, for facts only and with nothing copied: (1) O. Charnock Bradley, The Structure of the Fowl, 1915 (public domain), the chapter on the circulatory system, https://archive.org/details/structureoffowl00braduoft; (2) an open-access study of the heart and great arteries of the common pheasant, a close relative of the chicken, in a veterinary journal, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC12802561/; (3) Wikipedia, Bird anatomy, for the four chambers. A part only one of them names is not a part of this page. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
This bird heart diagram shows the heart of a chicken from the breast side, so the bird's right is on the left of the picture. First comes the outside, then the ventricles cut open.
Read the full guide
Four chambers
A bird's heart has two atria on top and two ventricles below. Blood from the body enters the right atrium and goes to the lungs from the right ventricle. It comes back to the left atrium and leaves for the body from the left ventricle.
What marks a bird's heart
The aorta arches over to the bird's right and gives off two brachiocephalic arteries. The valve on the right side is one thick flap of muscle, where a mammal has thin flaps. The left wall is several times thicker than the right.
Left and right are the bird's own. Seen from the breast, the right atrium is on the left of the picture.
In the cut view, find the thick wall first: that side is the left ventricle.
Questions and answers
How many chambers does a bird's heart have?
Four: a right and a left atrium on top, and a right and a left ventricle below. A mammal's heart has four chambers as well.
How is a bird's heart different from a mammal's?
The plan is the same, with four chambers. In a bird the aorta arches to the right side, two brachiocephalic arteries leave it, and the valve between the right atrium and right ventricle is a flap of muscle with no thin cusps.
Why is the left ventricle wall so thick?
The left ventricle pumps blood to the whole body, and the right one only to the lungs nearby. In pheasants measured for a 2026 study the left wall was three to four times as thick as the right.
Which way does a bird's heart point?
The apex, its pointed end, is directed toward the tail and a little to the left. The atria and the great arteries are at the other end, the base.