Levitra (vardenafil hydrochloride) is an erectile dysfunction agent that works by blocking a certain enzyme (phosphodiesterase-PDE5) used to treat erectile dysfunction (impotence). In the unlikely case that you experience an uncomfortable or protracted erection that lasts four hours or longer, stop taking Levitra immediately and seek medical attention to avoid long-term issues. If you experience any of the following serious side effects from taking Levitra, let your doctor know: shortness of breath; vision changes; lightheadedness, fainting; seizures (convulsions); nausea, sweating, and a general feeling of unwellness; chest pain or heavy feeling; pain radiating to your arm or shoulder; or sudden vision loss, ringing in your ears, or sudden hearing loss.