The main difference between single circulatory systems and double circulatory systems is that in the case of single circulatory systems, blood passes through the heart only once on each circuit around the whole of the blood circulation system of the animal.but the double circulatory systems blood is pumped twice. Once from the heart to the lungs and then from heart to rest of the body.
In the single circulation the deoxygenated blood from the whole body of the animal spammed into the heart. From the heart it goes to the gills and the oxygenated blood is pumped back into the body. This kind of circulation takes place in fishes. Conversely, in the case of double circulatory systems, blood passes through the heart twice during one complete circuit around the blood system through the body of the animal. double circulation the deoxygenated blood is collected from the body, goes to the lungs for the process of oxygenation and then this oxygenated blood comes back to the heart. The heart pumps back this oxygenated blood into the body tissues. In this type of circulation, as the blood passes through the heart two times, it is known as double circulation. It takes place in birds & mammals like human beings.