Heart of cockroach: Heart is present in the mid-dorsal side of the body. The heart is attached to the body wall by 12 pairs of alary muscles. The heart is divided into 13 funnel-shaped chambers, of which 3 lie in the thorax and 10 in the abdomen. Each chamber has a pair of openings at the sides called ostia. The ostia are guarded by valves which allow the flow of blood from pericardial sinus in to the heart but not in the opposite direction. During circulation blood flow in to the heart through ostia. The heart chambers contract one after the other rapidly and it is due to contraction and relaxation of alary muscles. This pushes the blood into the anterior aorta i.e. the anterior-most heart chamber. From aorta, the blood passes in the head sinus and into other sinuses. All the chambers of heart are interconnected and their openings is guarded by valves to maintain unidirection flow of blood.