Regurgitation is blood flow in the opposite direction from normal, as the backward flowing of blood into the heart or between heart chambers. Can be categorized by:

1. aortic: the backflow of blood from the aorta into the left ventricle, owing to insufficiency of the aortic semilunar valve; it may be chronic or acute.
2. mitral: the backflow of blood from the left ventricle into the left atrium, owing to insufficiency of the mitral valve; it may be acute or chronic, and is usually due to mitral valve prolapse, rheumatic heart disease, or a complication of cardiac dilatation. See also Mitral regurgitation.
3. pulmonic: the backflow of blood from the pulmonary artery into the right ventricle, owing to insufficiency of the pulmonic semilunar valve.
4. tricuspid: the backflow of blood from the right ventricle into the right atrium, owing to imperfect functioning (insufficiency) of the tricuspid valve.
5. valvular: regurgitation of the blood through the orifices of the heart valves owing to imperfect closing of the valves; see aortic, mitral, pulmonic, and tricuspid.

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