Two-Chambered Heart: Definition, Anatomy & Quiz

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The two-chambered heart is an interesting form of the primary circulatory organ, and exists primarily in animals that use gills for breathing. Find out why the two-chambered heart exists, and what makes it different from other types of hearts.

We also recommend watching Anatomy of the Heart: Blood Flow and Parts and Arrhythmia of the Heart: Terms, Definition & ECG Detection

The Two-Chambered Heart

The heart is the primary organ for circulation in larger animal species, including human beings. The purpose of the heart is to provide force for the pumping of blood throughout the animal's body, which allows for nutrients and oxygen to be delivered to tissues and waste materials to be removed.

The heart contains cardiac muscle, which is involuntarily controlled (the animal does not have conscious control over it) and works continuously throughout the life of the animal to drive circulation. This is an important function, but in different animals, can be achieved by different means.

Chambers of the Heart

Regardless of the organism, if it has a heart, then that heart will be divided into chambers, or specialized compartments. The two types of chambers are atria (receiving chambers) and ventricles (pumping chambers).

Typically, the atria are the first stops for blood entering the heart, and the ventricles are the chambers that push blood out of the organ. The organization of these chambers will differ depending on the needs of the system, particularly as it relates to breathing and respiration. Animals with two-chambered hearts are those that use gills to replenish oxygen in the blood supply, whereas animals that have three- or four-chambered hearts also contain lungs for respiration.

Fish and the Two-chambered Heart

Two-Chambered Heart and Circulation
Two chambered heart

The circulatory and respiratory systems are closely linked. Blood circulating through the body must go through the respiratory system for gas exchange (carbon dioxide exchanged for oxygen).

Fish have single circulation, which means that once blood leaves the gills, it is immediately sent to the rest of the animal's body. This is different from, say, the human heart, where blood leaving the lungs has to return to the heart before entering the rest of the body. This simple, single circulation doesn't require additional chambers to receive blood from the lungs, and therefore, does not need more than two chambers to pump blood.


The two-chambered heart is a simple organ that pumps blood for animals with gills and single circulation. Because blood leaves the gills and immediately circulates to the rest of the body, the heart does not require additional chambers beyond the first two. Fish and other animals with two-chambered hearts, therefore, have simpler circulatory systems than animals with lungs, and subsequently, three- and four-chambered hearts.

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