what is the first organ to develop in a fetus

The first organ to develop in a fetus is the heart. The development of the heart begins in the third week of gestation, and by the fourth week, the heart has established its four chambers. By the sixth week, the cardiac outflow separation and descent of the heart into the thorax occur, dividing the truncus arteriosus into the ascending aorta and pulmonary artery. This process is part of the organogenesis, which is the formation of organs from the primary germ cell layers established during gastrulation. The hearts early development is a crucial milestone in the growth and differentiation of tissues into organs during the embryonic period.