This observational study will involve analysis of data collected by the National Rare Disease Registry or medical records .The study will describe outcomes only in PAH(Pulmonary arterial hypertension) patients treated with sildenafil; there will be no comparison with another treatment group.

Approximately 100 adults with PAH will be recruited in China hospitals This NIS(non-interventional study) data will be recorded by a physician in the medical records, during the patients' clinical visits, and in the electronic Case Report Forms (CRF).

Inclusion Criteria:

• At least 18 years of age at study index date; (The index date (i.e., Day 1 of the study) is the date when the first sildenafil dose was actually taken, after Revatio® is approved by China authority)
• A diagnosis of PAH with a mean pulmonary artery pressure of ≥25 mmHg and a mean pulmonary capillary wedge pressure of ≤15 mmHg by right heart catheterization;
• Initiated sildenafil for the treatment of their PAH based on treatment suggestion from physician ;(Patients who have received sildenafil or are receiving sildenafil are eligible to participate in this study if they met the above inclusion criteria and were ready to start sildenafil (Revatio®) for treatment at screening;)
• Evidence of a personally signed and dated informed consent document indicating that the patient (or a legally acceptable representative) has been informed of all pertinent aspects of the study.

Exclusion Criteria:

• No

The study population will comprise patients with PAH (including idiopathic pulmonary arterial hypertension, PAH associated with connective tissue disease, and PAH associated with congenital heart disease patients) Patients must meet all of the inclusion criterias to be eligible for inclusion in this study