Viagra, or sildenafil, is a medication that increases blood flow by causing dilation of certain arteries. It was originally designed as a blood pressure medication and was later found to work mainly by increasing blood flow to the penis and thus helps maintain erections. Viagra is a fairly short-acting medication. In other words, if you take a pill, it will likely be out of your system in 12 to 24 hours. The main side effects that you might get by taking four Viagra pills would include lightheadedness, nausea, and an erection that would probably be difficult to get rid of. However, the next day or at least by the day after that, you would likely not have any effects of the Viagra.