A venous heart is another name for a fish's heart.
They are typically two-chambered, with a single auricle transporting oxygenated blood and a single ventricle transporting de-oxygenated blood.
It is primarily a type of close blood circulation.
Fish circulatory system:
There are accessory chambers, sinus venosus, and conus arteries or bulbous arteries.
The heart receives deoxygenated blood from all over the body, except the gills, into the sinus venosus and pumps it into the short artery, the ventral aorta, via the auricle, ventricle, and conus/bulbous.
The latter emits four or five pairs of afferent branchial arteries, which distribute blood from the gills to the dorsal aorta via efferent branchial arteries, epibranchial arteries, lateral dorsal aortae, and capillaries.
Blood returns to the heart via a vein.
Because blood only passes through the heart once in a complete circuit around the body, fishes are said to have a single circulation.
One disadvantage is that the narrow gill capillaries slow blood flow, resulting in low blood pressure in the body.
This slows the rate of oxygen delivery to cells and limits the metabolic rate that fish can achieve.
