Med express delivery service cialis is an effective, reversible, selective inhibitor of phosphodiesterase type 5 (PDE 5) specific to cyclic guanosine monophosphate (cGMP). When sexual stimulation causes local release of nitric oxide, inhibition of PDE 5 by Cialis leads to increase of cGMP levels in the cavernous body of penis. It results in the relaxation of arterial smooth muscles and blood flow to the tissues of the penis that causes erections. Cialis has no effect when sexual stimulation is absent. Cialis improves erection and let’s achieve a successful sexual intercourse. The drug acts for 36 hours. If sexual arousal is present the effect appears even after 16 minutes after the medication was taken. 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.