Imigran recovery buy online sildenafil affects the response to sexual stimulation. It acts by enhancing smooth muscle relaxation using nitric oxide, a chemical that is normally released in response to sexual stimulation. This smooth muscle relaxation allows increased blood flow into certain areas of the penis, which leads to an erection. A serious allergic reaction to this drug is very rare, but seek immediate medical help if it occurs. Most usual side effects of Apcalis are facial flushing (reddening), headaches, stomach upset, diarrhea, flu-like symptoms and nausea. In more rare cases low blood pressure, blurred vision and changes in color vision, and abnormal ejaculation may occur. Prolonged erections or priapism (painful erections lasting more than 6 hours) are also possible. If your erection is longer than 4 hours, seek for immediate medical help as it may permanently damage your penis. Aggravation of heart problems in patients with pre-existing heart disease using Apcalis was reported.