The heart is the first organ to form during development of the body. When an embryo is made up of only a very few cells, each cell can get the nutrients it needs directly from its surroundings. But as the cells divide and multiply to form a growing ball, it soon becomes impossible for nutrients to reach all the cells efficiently without help. The cells also produce waste that they need to get rid of. So the blood and circulatory system, powered by the heart, together form the first organ system to develop. They are essential to carry nutrients and waste around the embryo to keep its cells alive.