Increased pressure in the circulation of the lung, also called pulmonary hypertension (PH), often causes shortness of breath. There are many different reasons that may increase the pressure in the lungs, such as diseases of the heart,pulmonary or rheumatological diseases. A rare but very important cause is a disease of the pulmonary vessels called pulmonary arterial hypertension (PAH).Initially a cardiac ultrasound is performed to estimate the pressure in the lung. However, the most important diagnostic step is the performance of a right heart catheter. Upon diagnosis, a specific therapy can be initiated.