What is an advantage of having a 2 chambered heart?

A 2-chambered heart, found in fish, allows for a more efficient circulation of blood in aquatic environments. This simpler structure enables a continuous flow of oxygenated blood to the gills for respiration and then directly to the body, optimizing oxygen delivery. Additionally, the heart's design reduces the energy expenditure required for circulation, which is advantageous in water where oxygen levels can vary.