Gain a better understanding of medical terminology by searching our dictionary of more than 1,300 terms.


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  • Hashimoto's thyroiditis

    A degenerative autoimmune disease of the thyroid gland that ultimately results in a marked reduction in the amount of thyroid…

  • hay fever

    Allergic sensitivity to certain mold spores and pollens. Allergic reaction includes sneezing, itchy eyes, sore throat and runny nose.

  • heart

    The hollow, muscular organ responsible for pumping blood through the circulatory system.

  • heart block

    A condition in which electrical impulses aren’t properly transmitted from the heart’s upper to the lower chambers.

  • heart failure

    Inability of the heart to adequately pump blood.

  • heartburn

    Indigestion. A burning sensation in the chest caused by a reflux of acid into the esophagus or too much acid…

  • heat exhaustion

    Headache, profuse sweating, weakness, muscle cramps, nausea and vomiting caused by excessive exposure to heat.

  • heat stroke

    A serious failure of the body’s heat-regulating mechanism resulting from excessive exposure to intense heat. Also called sunstroke.

  • hemangioma

    A tumor or swelling that’s composed of blood vessels.

  • hematemesis

    The vomiting of blood.

  • hematology

    The branch of medicine that pertains to blood and the organs involved in forming blood.

  • hematoma

    A tumor-like mass of coagulated blood in the soft tissues. A contusion or bruise.

  • hematuria

    The presence of blood in the urine.

  • hemiplegia

    Paralysis (loss of feeling or movement) of one side of the body.

  • hemochromatosis

    A disorder of iron metabolism characterized by excessive amounts of iron in the skin, liver and other tissues.

  • hemoglobin

    The oxygen-carrying molecule in red blood cells.

  • hemolysis

    The destruction of red blood cells.

  • hemophilia

    An inherited disorder, nearly always in males, in which one of the normal blood-clotting factors is deficient.

  • hemoptysis

    A cough that produces blood.

  • hemorrhage

    Severe bleeding, usually from damage to a blood vessel.

  • hemorrhoid

    An enlarged vein inside or just outside the rectum.