Highlights of the Early Heart

The heart is the first organ to form in a developing baby. The heart starts beating 22 days after conception.¹ By 24 days, the heartbeat can be measured using transvaginal ultrasound technology in most viable pregnancies.² Over the next four weeks, the average heart rate rises from 98 beats per minute at 3 ½ weeks to 175 beats per minute at 7 weeks post conception.³

The heart starts as two tubes, which fuse together and fold during the fourth week, forming an s-curve. In the fifth week, two sections become the atria, and in the sixth week the ventricles form. The heart reaches its final shape by the eighth week, with two atria, two ventricles, and circulatory blood vessels, although these blood vessels mostly bypass the liver and lungs to help the embryo get oxygenated blood from the umbilical cord to the rest of the body.⁴