Serotonin (5-hydroxytryptamine, 5-HT) exerts its many physiological effects through 13 distinct receptor subtypes in humans. These subtypes fall into seven structurally-defined classes (5-HT1 to 5-HT7). 5-HT2B receptors are expressed in the liver, kidney, lung, heart, pancreas, spleen, brain, spinal cord, gastrointestinal tract, placenta, and coronary and pulmonary arteries. It has also been reported in embryonic mouse heart. This receptor has been used as a target for developing drugs to treat migraine, anxiety, and irritable bowel syndrome.