Answer
The primitive heart begins to contract by the 22nd day of gestation
Work Step by Step
The heart begins to develop from mesoderm on Day 18-19 of fertilization. First some mesodermal germ cells differentiate into cells of the cardiogenic area. Further, some of these cells form two elongated cardiogenic cords. Later these cords hollow out to form paired endocardial tubes. The primitive heart is formed by fusion of the two endocardial tubes at Day 21 after fertilization. The primitive heart begins to beat on the 22 day of gestation
