5-HT2B, a Serotonin Receptor, activates phospholipase C upon binding serotonin, which results in a rise in intracellular calcium. It is known that 5-HT2B regulates cardiovascular function during development and in adulthood; mice lacking functional 5-HT2B receptors died of heart defects during gestation or neonatally, and adult mutant mice displayed cardiopathy, including myocyte disarray and ventricular dilation. Abnormal vascular proliferation causes an increase in pulmonary blood pressure, which is associated with an increase in 5-HT2B receptor, resulting in the development of pulmonary hypertension. It has also been reported that the 5-HT2B is involved in cell-cycle regulation via interaction with tyrosine kinase pathways. 5-HT2B receptors may have a role in the initiation of migraine headaches, and selective antagonists may prove therapeutic in migraine treatment. 5-HT2B receptor is expressed in many tissues including human 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 and spinal cord. ESTs have been isolated from heart/melanocyte/uterus, kidney, prostate, skin, and thyroid libraries.