Sildenafil is a medication used to treat erectile dysfunction and pulmonary arterial hypertension.Common side effects include headaches and heartburn, as well as flushed skin. Caution is advised in those who have cardiovascular disease. Rare but serious side effects include prolonged erections, which can lead to damage to the penis, sudden-onset hearing loss. Sildenafil should not be taken by people who take nitrates such as nitroglycerin, as this may result in a severe and potentially fatal drop in blood pressure. It acts by inhibiting cGMP-specific phosphodiesterase type 5 (PDE5), an enzyme that promotes degradation of cGMP, which regulates blood flow in the penis. Do not exceed 1 tablet in 24 hours, best taken on advice of your treating physician.