A type of blood circulation system in which the blood flows through the heart twice. In this type of circulation, the pulmonary circulation is separate from the systemic circulation.
In this circulation, the heart consists of: the right side that pumps deoxygenated blood into the pulmonary section and the left side that pumps oxygenated blood into the systemic circulation. This is common among mammals and birds. This is in contrast to animals that have only one circulation system such as fish.
Compare: single cycle circulation