Right atriumIt receives blood from the anterior and posterior vena cava. Before birth, much of the blood from the posterior vena cava passes on through the foramen ovale.
Left atriumBefore birth it fills mostly through the foramen ovale. This is because little blood comes back from the lungs.
Right ventricleIt pumps blood into the pulmonary trunk. On this face the groove between the two ventricles lies near the heart's left border.
Left ventricleIt pumps blood into the aorta, and so to the whole body.
Pulmonary trunkIt leaves the right ventricle. Before birth most of its blood goes on through the ductus arteriosus to the aorta, and only a little goes to the lungs.
Pulmonary arteriesThe two branches of the pulmonary trunk, one to each lung. Before birth they are smaller than the ductus arteriosus.
Ductus arteriosusA short vessel from the pulmonary trunk to the aorta. It lets blood bypass the lungs. After birth it closes and becomes a cord, the ligamentum arteriosum.
Aortic archThe aorta leaves the left ventricle and curves toward the pig's left. In the pig two arteries branch from the arch.
Brachiocephalic arteryThe first branch of the aortic arch. It gives off the common carotid arteries to the head and goes on to the right front leg.
Left subclavian arteryThe second branch of the aortic arch. It supplies the left front leg. Older books call it the left brachial artery.
Anterior vena cavaBrings blood from head, neck and front legs to the right atrium. Also called the cranial or superior vena cava.
Posterior vena cavaBrings blood from the rear of the body to the right atrium. Before birth it brings the blood from the umbilical vein too.
The route before birth 7
Foramen ovaleAn opening in the wall between the two atria. Blood passes through it from the right atrium to the left, and a flap stops it flowing back. It closes after birth.
Dorsal aortaThe aorta after the arch. The ductus arteriosus joins it, and it carries blood to the rear of the body.
Umbilical arteriesTwo arteries that carry blood out through the cord to the placenta. They leave the end of the aorta by way of the internal iliac arteries.
Umbilical cordIt joins the fetus to the placenta. It holds the two umbilical arteries and the one umbilical vein.
Umbilical veinCarries oxygen-rich blood from the placenta through the cord to the liver.
LiverThe umbilical vein enters it. Some of the blood passes through the liver and much of it goes past through the ductus venosus.
Ductus venosusA temporary vessel in the liver. It carries blood from the umbilical vein straight on to the posterior vena cava.
How this list was compiled: Every name checked on 2026-09-30. For the pig: Septimus Sisson, The Anatomy of the Domestic Animals (1914), the heart and arteries of the pig and the section on the foetal circulation, https://archive.org/details/anatomyofdomesti00siss, and two fetal pig dissection guides read through the Internet Archive's full-text search: F. Bohensky, Photo Manual and Dissection Guide of the Fetal Pig (1978), https://archive.org/details/photomanualdisse0000fred_u2p3, and D. G. Smith and M. P. Schenk, Dissection Guide and Atlas to the Fetal Pig, https://archive.org/details/dissectionguidea0000unse. The three fetal shunts and what becomes of them after birth: OpenStax, Anatomy and Physiology 2e, section 20.6, https://openstax.org/books/anatomy-and-physiology-2e/pages/20-6-development-of-blood-vessels-and-fetal-circulation. 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 fetal pig heart diagram shows the heart from the front, then the route the blood takes before birth. A fetus gets its oxygen from the placenta and not from its lungs, so three shortcuts carry blood past the lungs and the liver.
Read the full guide
The heart from the front
As a pig heart diagram it has the usual four chambers, both venae cavae, the pulmonary trunk and the aortic arch. Two things are the pig's own: the arch has two branches, the brachiocephalic artery and the left subclavian artery, and before birth the ductus arteriosus joins the pulmonary trunk to the aorta.
The route before birth
Follow the arrows. Blood comes in from the placenta by the umbilical vein, passes the liver through the ductus venosus, and reaches the right atrium by the posterior vena cava. Much of it crosses the foramen ovale to the left side. It leaves by the dorsal aorta and the two umbilical arteries.
To find the ductus arteriosus, follow the pulmonary trunk up from the right ventricle until it meets the aorta.
The foramen ovale is inside: open the right atrium and look at the wall it shares with the left.
Questions and answers
How is a fetal pig's heart different from an adult's?
It has two shortcuts past the lungs. The foramen ovale is an opening between the two atria. The ductus arteriosus is a short vessel from the pulmonary trunk to the aorta. Both close after birth, when the lungs start to work.
What does the ductus arteriosus become after birth?
It closes and turns into a cord of tissue called the ligamentum arteriosum, which still joins the pulmonary trunk to the aorta in the adult heart.
How many branches come off the aortic arch in a pig?
Two. The brachiocephalic artery comes first and supplies the head and the right front leg. The left subclavian artery comes second and supplies the left front leg.
What is the ductus venosus?
A temporary vessel in the liver. It carries much of the blood from the umbilical vein straight to the posterior vena cava, so that blood goes to the heart without passing through the liver.