What does they have three chambered hearts mean?

Answer 1

Human beings, and mammals in general, have a certain type of heart, with four sections, called chambers. A chamber that receives blood is called an atrium (they were once called auricles), and a chamber that pumps blood is called a ventricle. Two chambers serve the function of receiving blood from the lungs and pumping blood to the lungs, and two other chambers receive blood from the rest of the body and pump blood to the rest of the body. Ambhibians and reptiles have a three chambered heart. Their hearts have only three sections, and their circulatory system is therefore somewhat simpler than that of mammals, and somewhat less efficient.