Evolution of heart in vertebrates?

The evolution of the heart in vertebrates is a complex process that has occurred over millions of years. The earliest vertebrates, such as fish, had simple, two-chambered hearts that pumped blood in a single loop through the body. As vertebrates evolved and diversified, their hearts became more complex and developed additional chambers to improve efficiency and oxygenation of the blood.

In amphibians, such as frogs and salamanders, the heart is three-chambered, with two atria and one ventricle. This allows for some separation of oxygenated and deoxygenated blood, but there is still some mixing in the single ventricle.

In reptiles, such as snakes and lizards, the heart is partially divided into four chambers, with two atria and two ventricles. This further separates oxygenated and deoxygenated blood, allowing for more efficient oxygenation of tissues.

In birds and mammals, the heart is fully divided into four chambers, with two atria and two ventricles completely separated by a septum. This allows for complete separation of oxygenated and deoxygenated blood, resulting in more efficient oxygenation of tissues and higher metabolic rates.

Overall, the evolution of the vertebrate heart has been a gradual process of increasing complexity and efficiency, leading to the highly specialized four-chambered hearts found in birds and mammals today.