Sildenafil

Sildenafil can help men achieve stronger and longer-lasting erections by improving blood flow. Erections occur when blood vessels near the penis dilate, allowing blood to fill the smooth muscle in the penis, making it harder. However, if you have ED, these vessels remain constricted, preventing sufficient blood flow and making it difficult to achieve or maintain an erection.
PDE5 is the enzyme responsible for this vessel constriction. Sildenafil is a PDE5 inhibitor, meaning that it blocks this enzyme. This in turn improves blood flow, resulting in better, harder erections.
As with other erectile dysfunction medications, Sildenafil only works if you are sexually stimulated. You and your partner will still need foreplay to prepare for sex, just as you would without the medication.