You may not have heard of the term sildenafil citrate, but you are more than likely to be aware of the brand name product it is sold as on the market. This is the actual name of the male impotence or erectile dysfunction drug known as Viagra. Sildenafil citrate is also sold under other trade names, including Revatio. The drug works by increasing blood flow to the penis, thus enabling men to enjoy longer and harder erections. However, it must be taken in conjunction with sexual stimulation in order to be effective. The doses of sildenafil citrate include 25 mg, 50 mg and 100 mg, and they are sold as diamond-shaped blue tablets.