<P> Heart development refers to the prenatal development of the human heart . This begins with the formation of two endocardial tubes which merge to form the tubular heart , also called the primitive heart tube , that loops and septates into the four chambers and paired arterial trunks that form the adult heart . The heart is the first functional organ in vertebrate embryos , and in the human , beats spontaneously by week 4 of development . </P>
when does the heart develop and begin pumping blood
week 4 of development