How the structure of a fish heart differs from the human heart?

The structure of a fish heart is simpler than that of a human heart, consisting of only two chambers: one atrium and one ventricle. This design allows for a single circulatory system, where blood is pumped from the heart to the gills for oxygenation and then directly to the rest of the body. In contrast, the human heart has four chambers—two atria and two ventricles—enabling a double circulatory system that separates oxygen-rich and oxygen-poor blood, allowing for more efficient oxygen delivery to tissues. Additionally, the human heart's complexity supports higher metabolic demands compared to the simpler fish heart.