Vasodilator It can treat erectile dysfunction. It can also treat high blood pressure in the lungs (pulmonary arterial hypertension). Brands: Viagra and Revatio Availability: Prescription needed Pregnancy: No known risks Alcohol: Avoid. Very serious interactions can occur Erectile dysfunction is when a man has difficulty getting an erection. ... It happens when not enough blood flows to the penis, preventing an erection. ... VIAGRA works for men with erectile dysfunction (ED) by increasing blood flow to the penis so you can get and keep an erection hard