what is significant about a 3 chambered heart?

Most reptiles and amphibians have a three chambered heart. This circulatory set up allows both oxygenated and non-oxygenated blood to mix in the single ventricle. In organisms that are not amphibians or reptiles, this can be a problem. Amphibians and reptiles cope with the lesser oxygen count via their hearts, by also taking in oxygen through their skins.