How do lungfish lungs and gills work side by side in circulation?

Lungfishes possess a specialized circulatory system that allows their lungs and gills to function in tandem, a significant evolutionary development that mirrors the systems found in amphibians.1

The heart of a lungfish is partially divided, allowing it to keep oxygenated and deoxygenated blood largely separate. The left side of the atrium receives oxygenated blood from the lungs, while the right side receives deoxygenated blood from the body. A complex spiral valve within the heart and a subdivided ventral aorta ensure that blood is efficiently routed: oxygenated blood is directed toward the anterior arterial arches to reach the head, while deoxygenated blood is sent to the posterior arches to be oxygenated in the lungs.1

While lungfishes retain four branchial arches (gills), their arrangement is modified to accommodate air breathing. In some species, the gills may be reduced, and blood vessels may bypass the gill capillaries entirely. This dual-system approach allows lungfishes to thrive in oxygen-poor environments by switching between aquatic and atmospheric respiration as needed.123