The investigators propose a prospective, observational study to determine the impact of OSA and associated physiological parameters on clinical outcomes in patients with pulmonary hypertension. The prevalence, phenotypes, and predictors of OSA in the setting of pulmonary hypertension will also be investigated. Adult patients diagnosed with pulmonary hypertension by right heart catheterization are eligible. Recruited patients will undergo an overnight cardiorespiratory study using a Level III portable device before hospital discharge. The cardiorespiratory tracings during sleep will be analyzed and audited by a certified sleep physician. The patients will be divided into two groups based on the apnea-hypopnea index (AHI): OSA (AHI ≥ 5) and non-OSA (AHI\<5) groups. Hypoxemic parameters such as time percentage spent with oxygen saturation below 90% and nadir oxygen saturation were all collected. Baseline clinical characteristics, such as the Epworth sleepiness scales, were also obtained. The primary endpoint of this study was clinical worsening (CW), defined as the composite event of a reduction in exercise capacity, worsening in World Health Organization functional class, non-elective hospitalization for pulmonary hypertension, or all-cause mortality. Secondary endpoints include individual outcomes of clinical worsening and all-cause mortality.