Cialis is the brand name of tadalafil, a prescription drug for men used to treat erectile dysfunction (ED). Cialis helps to increase blood flow to the penis, enabling a man to hold an erection for a longer duration. Men who use Cialis should be healthy enough to have sex, not take nitrates for chest pain (angina), and consult a physician if an erection lasts more than four hours or is painful. Cialis 20 mg Tablet relaxes the smooth muscles present in the wall of blood vessels and helps in increasing the flow of blood in certain specific areas of the body. It is used for the treatment of erection disorders, prostate gland enlargement and Pulmonary Hypertension (high blood pressure of blood vessels connecting the lungs and the heart).