Heart Formation

The embryo's heart is the first organ that forms. It is derived from two primitive heart tubes. Between days 18 to 30, the primitive heart tubes fuse together, bend and twist to form a simple version of the heart. About half way through this process, the heart starts to beat. At 2 months, the heart bears a close resemblance to what it will look like after the baby's born. The resemblance is only superficial since the inside of the heart is different in both form and function. In a newborn's heart, oxygen-poor blood from the body enters the right atrium, goes to the right ventricle where it is pumped to the lungs to become rich with oxygen. From the lungs, the blood flows back to the heart filling the left atrium then enters the left ventricle. The left ventricle pumps the oxygen rich blood through the aorta, which carries it to the rest of the newborn's body. The fetal heart has the same basic components as the newborn heart, but there are a couple important differences. Because the placenta is providing all of the oxygen the fetus requires, its lungs are not needed to perform this task. Much of the fetus' blood is detoured away from the lungs through two openings or connections the foramen ovale, which connects the right and left atria, and the ductus arteriosus, which connects the aorta and the pulmonary artery. These two important connections will remain open up until the time of birth. Within thirty minutes after the baby's first breath, the ductus arteriosus will completely close, and the flap of the foramen ovale will shut off like a valve. This happens because of an increase in pressure on the left side of the heart, and a decrease on the right side. These changes in the heart anatomy cause the blood to flow to the lungs, which will take over their lifelong job of supplying oxygen to the body.

Heart Formation

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Review Date: 7/4/2019

Reviewed By: John D. Jacobson, MD, Professor of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda Center for Fertility, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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