Table 1. WHO classification of PH.

WHO group	Definition
Group 1	PAH: idiopathic, heritable, drug-related, and connective tissue PAH (such as scleroderma), portopulmonary, HIV, schistosomiasis
Group 2	Pulmonary hypertension secondary to left heart disease: diastolic HF, systolic HF, valvular HF
Group 3	PH due to chronic lung disease and/or chronic hypoxemia
Group 4	Chronic thromboembolic disease
Group 5	PH which is multifactorial

WHO, World Health Organization; PH, pulmonary hypertension; PAH, pulmonary arterial hypertension; HIV, human immunodeficiency virus; HF, heart failure.