Sildenafil for pulmonary hypertension.

Pulmonary Hypertension (PH) can be either of unknown aetiology (primary pulmonary hypertension (PPH)) or due to a known underlying cause (secondary pulmonary hypertension (SPH). Pulmonary arteriolar vasoconstriction is considered to be an important characteristic of PH. Therapies which aim to vasodilate are used to treat pulmonary hypertension.