Q. Who among the following have venous heart?
Answer: Fishes
Notes: In most fish, the heart consists of four parts, including two chambers and an entrance and exit. The first part is the sinus venosus, a thin-walled sac that accumulates blood from the fish's veins before permitting it to flow to the second part, the atrium. The atrium is a large muscular chamber, present as a one-way passage, that sends blood to the third part, the ventricles. The ventricle is a thick-walled, muscular chamber that pumps the blood, first to the fourth part, bulbus arteriosus. The bulbus arteriosus is a large tube, and then out of the heart, which attaches to the aorta, through which blood flows to the gills for oxygenation.