Sea stars don't have a heart. They are designed in a way that they don't need blood instead they have a vascular system. They have a haemal system and the vessels form rings around the mouth, around the digestive system, and near the aboral surface. The three vessels in the haemal system of sea stars are the hyponeural haemal ring, the gastric ring, and the genital ring. Their heart-like circulatory beats six times per minute as per sea star facts. Sea stars have very little respiratory function. Some sea stars have no respiratory function in their vessel