Viagra, or sildenafil, is used to treat erectile dysfunction, according to MayoClinic.com. Viagra belongs to a group of medications that increase nitric oxide, a chemical that relaxes and opens the blood vessels in the body. This helps men get an erection but also causes unwanted effects. Viagra makes an erection possible during sexual stimulation but doesn't increase sex drive.
Cardiac Risks
Men with pre-existing heart disease face potential cardiac risks with sexual activity. Because of this, Viagra should generally not be taken by men who have an underlying cardiovascular status that makes sex inadvisable, according to the National Institutes of Health website, DailyMed. Certain conditions can increase risk of adverse cardiac effects related to the opening and relaxing of blood vessels, called vasodilation. Included are aortic stenosis, impaired autonomic control of blood pressure, a history of stroke, heart attack or abnormal heart rhythm, resting hypotension or hypertension, unstable angina and some disorders of the retina.
Dangerously Low Blood Pressure
Viagra is a vasodilator. When used at the same time as other vasodilators, a dangerously low blood pressure can result, leading to dizziness, lightheadedness and fainting. Vasodilators include medication used for treating chest pain, such as isosorbide, nitroglycerin, Imdur, Nitrostat, Transderm Nitro and Nitro-Bid. Some illegal drugs and "poppers," such as amyl nitrate and butyl nitrate, cause vasodilation and should be avoided.
Priapism
Viagra can cause priapism, a disorder characterized by a prolonged and painful erection that can permanently damage the penis. An erection lasting four hours or longer requires medical attention, MayoClinic.com says. If you have conditions affecting the penis--such as angulation, cavernosal fibrosis or Peyronie's disease--or have conditions that may increase risk of priapism, such as sickle cell anemia, multiple myeloma or leukemia, use Viagra with caution.
Common Side Effects
According to MayoClinic.com, common side effects from Viagra include headache, stuffy nose, temporary "blue vision" and other temporary visual changes and indigestion.
Loss of Hearing or Vision
Sudden loss of hearing or vision after taking Viagra has been reported, but evidence fails to show if the cause was Viagra or a pre-existing condition, MayoClinic.com says. Sudden loss of hearing or vision requires immediate medical attention.
