disease, pulmonary vasculitis, collagenoses, or pulmonary thromboembolism.In cases of idiopathic PAH (IPAH), one-, three-, and five-year survival rates after symptom onset are 68%, 48%, and 34%, respectively.(3) Calcium antagonist drugs have a known pulmonary vasodilator effect, decreasing pulmonary pressure and increasing the survival and quality of life of patients with IPAH.(4) However, less than 20% of these patients, corresponding to those that present pulmonary vasoreactivity, should use this medication.(5) For patients not presenting pulmonary vasoreactivity, the use of calcium IntroductionPulmonary arterial hypertension (PAH) is defined as mean pulmonary artery pressure (MPAP) > 25 mmHg at rest and > 30 mmHg during exercise.(1) Observations suggest that vasoconstriction plays an important role in the pathogenesis of PAH. This disease is characterized by medial hypertrophy of pulmonary arterioles, decreased endothelial production of vasoconstrictors (prostacyclin and nitric oxide), and increased production of the vasoconstrictor endothelin.(2) Pulmonary arterial hypertension (PAH) is classified as idiopathic, when the cause is unknown, or secondary, when it is associated with pulmonary parenchymal diseases, heart Testing pulmonary vasoreactivity* AbstractPulmonary arterial hypertension is classified as idiopathic or secondary (associated with collagenoses, heart disease, portal hypertension, pulmonary thromboembolism, and pulmonary vascular diseases). Pulmonary vasoreactivity should be tested in order to define the best treatment option. Of the many drugs that have been used to test pulmonary vasoreactivity, inhaled nitric oxide is the best choice, due to its specific pulmonary effect and very short half-life (5-10 s). The results of this test identify candidates for heart surgery among patients with congenital heart disease and candidates for the use of calcium antagonists among patients with other forms of pulmonary arterial hypertension. Performing and interpreting the results of such tests are a great responsibility, since mistakes can lead to incorrect treatment decisions, resulting in the death of patients.Keywords: Hypertension, pulmonary/diagnosis; Nitric oxide/diagnostic use; Administration, inhalation. ResumoA hipertensão arterial pulmonar é classificada como idiopática ou secundária (associada a colagenoses, cardiopatias, hipertensão portal, tromboembolismo pulmonar e doenças da vasculatura pulmonar). O teste de vasorreatividade pulmonar é indicado para definir a melhor opção terapêutica. Muitas drogas têm sido utilizadas para a realização desse teste, sendo o óxido nítrico inalado a melhor opção, por apresentar ação específica pulmonar e meia vida muita curta (5-10 s). O resultado desse teste identifica candidatos à cirurgia cardíaca nas cardiopatias congênitas e candidatos ao uso de antagonista de cálcio nas outras formas de hipertensão pulmonar. A realização e interpretação do teste de vasorreatividade pulmonar exigem grande responsabilidade, e erros podem levar a decisões erradas e à ocorr...