Difficulty in penile erection taking sildenafil, need to be through sexual stimulation before the penis can be erected, specific to clarify the causes of penile erection difficulties, under the guidance of the doctor symptomatic treatment. Sildenafil is a drug used to treat male erectile dysfunction, is a phosphodiesterase type V inhibitor, can make the increase in nitric oxide content in the penis, so that the level of cyclic guanosine in the smooth muscle cells of the penis, stimulate the cavernous body of the penis, so that the cavernous body of the penis is congested and swollen, so as to achieve the effect of prolonging the duration of sexual life. After taking sildenafil may appear flushing, blurred vision, nausea and other symptoms, usually disappear on their own, avoid and nitrate drugs taken together, easy to produce low blood pressure, blood pressure abnormalities, severe renal impairment and other people are prohibited to take. Drugs should be taken under the guidance of a doctor to avoid damage to the body.