What is the difference between double circulation and single circulation found in vertebrates?

Double circulation involves two separate circuits for blood flow: the pulmonary circuit, which carries deoxygenated blood from the heart to the lungs for oxygenation, and the systemic circuit, which delivers oxygenated blood from the heart to the rest of the body. In contrast, single circulation, found in some fish, involves a single circuit where blood flows from the heart to the gills for oxygenation and then directly to the rest of the body before returning to the heart. This means that in single circulation, blood passes through the heart only once per complete circuit, whereas in double circulation, it passes through the heart twice. Consequently, double circulation allows for more efficient oxygen delivery and higher metabolic rates in terrestrial vertebrates.