How are amphibians able to mostly keep oxygenated and deoxygenated blood separated and prevent mixing in the ventricle?

The amphibians are able to keep mostly oxygenated and deoxygenated blood separated and prevent it from mixing in the ventricle is likely because of their intermediate circulatory system in which both atria has the role of dumping it through a single ventricle, making the oxygenated and deoxygenated blood to be separated and prevent it from mixing though sometimes it is less efficient because mixing sometimes occurs.