Erectile dysfunction refers to a condition when the man cannot get his erection or is unable to keep it up. This may happen because stress alcoholism drug abuse etc. It happens when blood refuses to flow into the penis. It is a very common condition among older men. People often treat it by taking a sildenafil. Sildenafil (sold under different names) is a medication that restores blood flow to the penis and solves the problem of erectile dysfunction. According to a research in National Institutes of Health L-Citrulline an amino acid found in watermelon can also regulate blood flow to the penis. While the study is still under review and is not