Which of the following vertebrates has the most simple structured heart

Answer Details

Fish have the most simple structured heart among the given options. The fish heart consists of two chambers, an atrium and a ventricle. The atrium receives deoxygenated blood from the body and pumps it into the ventricle, which in turn pumps the blood to the gills for oxygenation. This is in contrast to the more complex heart structures of the other options, which have more chambers and a more sophisticated system for circulating oxygenated blood throughout the body.