Table 2. Current pulmonary hypertension classification (6).

Group	Subgroup
Group 1: pulmonary arterial hypertension	1.1 Idiopathic PAH
	1.2 Heritable PAH
	1.3 Drug- and toxin-induced
	1.4 Associated with connective tissue disease, human immunodeficiency virus infection, portal hypertension, congenital heart disease and schistosomiasis
Group 2: PH secondary to left heart disease	2.1 PH due to heart failure with preserved left ventricular ejection fraction
	2.2 PH due to heart failure with reduced left ventricular ejection fraction
	2.3 Valvular heart disease
	2.4 Congenital/acquired cardiovascular conditions leading to post-capillary PH
Group 3: PH secondary to lung diseases +/- hypoxia	3.1 Obstructive lung disease
	3.2 Restrictive lung disease
	3.3 Other lung disease with mixed restrictive/obstructive pattern
	3.4 Hypoxia without lung disease
	3.5 Developmental lung disorders
Group 4: Chronic thromboembolic PH
Group 5: PH with unclear multifactorial mechanism	5.1 Haematological disorders
	5.2 Systemic and metabolic disorders
	5.3 Others
	5.4 Complex congenital heart disease

PAH, pulmonary arterial hypertension; PH, pulmonary hypertension.