The heart is the first organ to develop during the formation of a human embryo. This occurs as early as the third week of gestation. By the seventh week, a complete heart with four chambers is formed.
The cardiovascular system, which includes the heart, is the first organ system to develop in the process of organogenesis.
Note: While the heart is the first organ to form in a human embryo, this does not mean it's the first organ to ever exist. The evolution of organs is a complex process with a long history.
