Painstaking research led to the discovery of gene mutations responsible for heritable forms of pulmonary arterial hypertension (PAH). Mutations in the gene BMPR2, which codes for a cell surface receptor (BMPRII), cause the approximately 80% of heritable cases of PAH. Less commonly mutations in ALK1, CAV1, ENG, and SMAD9, and newly discovered mutations in KCNK3, may cause heritable PAH. Other family members of many patients diagnosed with idiopathic PAH may be diagnosed with PAH. Genetic counseling and testing should be offered to patients diagnosed with heritable or idiopathic PAH.