Table 1. The World Health Organization classification of pulmonary hypertension2) .

WHO classification	Description
Group 1	Pulmonary artery hypertension
Group 2	PH due to left heart disease
Group 3	PH due to lung disease
Group 4	Chronic thromboembolic PH
Group 5	PH with unclear and/or multifactorial mechanisms

PH: pulmonary hypertension, WHO: World Health Organization.