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, placing it in the sixth gestational week.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 110 beats per minute at at the beginning of 6 weeks gestation to 173 beats per minute at the end of 9 weeks gestation.³

The heart starts as two tubes, which fuse together and fold during the sixth week, forming an s-curve. In the seventh week, two sections become the atria, and in the eighth week the ventricles form. The heart reaches its final shape by the tenth 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