The heart of mammals have four chambers. In fish, the heart only has one atrium and one ventricle. The four compartments are arranged sequentially. The heart of fish have two chambers. The sinus venosus (first accessory chamber), collects deoxygenated blood through the incoming hepatic and cardinal veins. The fish heart has one atrium and one ventricle; this is in contrast to the human (mammalian) heart that … Fish possess the simplest type of true heart a two-chambered organ composed of one atrium and one ventricle.

6.1a-b). Fish have a two-chambered heart consisting of one atrium to receive blood and one ventricle to eject it. Blood is pumped from the ventricle through the conus arteriosus to the gills. The heart of fishes consists of four chambers, a sinus venosus, an atrium, a ventricle and a conus or a bulbus arteriosus (Fig.
The first chamber is called the atrium, which receives blood that has been deprived of oxygen. A rudimentary valve is located between the two chambers. On the next page, you will see that the arrangement of the circulation in the fish is based on a fine balance. The blood then passes into the second chamber, the ventricle.

There are two chambers in a fish heart. The conus arteriosus is like the aorta in other species.

Some authors considered atrium and ventricles as the chambers of heart while some considered sinus venosus and conus arteriosus also as the chambers of the heart.
At the gills, the blood receives oxygen and gets rid of carbon dioxide. The heart of reptiles and amphibians have three chambers. Entry and exit compartments are often referred as accessory chambers. The cusps are attached to the heart wall along their lower edge and one side, with the free edges coming together or separating to …

The oxygen-depleted blood that returns from the body enters the atrium, and then the ventricle, and is then pumped out to the gills where the blood is oxygenated, and then it continues through the rest of the body. The : The heart has four chambers that are separated from each other by one-way valves. The fish heart - the pump The heart is the pump that generates the driving pressure for the circulation of blood (P1 = the arterial pressure in the previous pages). These valves consist of thin, cup-shaped membranes called cusps.