1. Introduction: In one of the previous study held at Massachusetts Male Aging this study shows that greater than 50% men shows the symptoms of Erectile Dysfunction (Feldman HA, 1994). The Erectile Dysfunctions is the inability to maintain the erect penis for sufficient time for the sexual intercourse. In an epidemiological survey it is seen that one in five men experience impairment in erection. These impairment are mostly due psychogenic and in older age it is mainly due to organic cause. The sexual dysfunctions are still the considered a taboo subject to be discussed in the society. But with the advancement in the scientific knowledge and awareness among the public can help solves these problems. The development of first ever effective oral drug for erectile dysfunction has changed the life of man who suffer from this problem. Many other risk factors are linked to the prevalence of erectile dysfunction they include, cardiovascular disease, hypertension, diabetes, hypercholesterolemia (modern maturity sexuality study, 1999). Historically there is very limited knowledge about the mechanism of erection is known. This limitation caused the treatment of ED though vacuum-constriction devices. The invention of PDE-5 inhibitors has revolutionized the medical horizon of ED treatment. The PDE-5 inhibitors drug sildenafil is the most effective oral drug treatment for ED. This drug was discovered during the heart clinical trial by the researchers who found that this drug is more effective in erectile dysfunction. Later 2 other similar products Vardenafil and Todalafil were introduced to the market. Both Sildenafil and Vardenafil differ slightly in their basic structure while there is marked difference in the molecular structure of Todalafil. This structural difference led to different pharmacokinetics properties of the drug. Now whenever a new drug is developed there arouse the questions about the efficacy and side effects of newly developed drug. The more efficacious drug have better effect on ED treatment. 2. Physiology of Erections: The physiology of the erection depends upon the neurochemical and endocrinological mechanisms. When man become sexually aroused a secondary chemical messenger relaxes the smooth muscles of corpus cavernosum. This whole process is regulated by neuroanatomical connection between peripheral and central nervous system (Moreland et al. 2001). There is time of excitement followed by plateau phase an orgasmic phase, a resolution and then a refractory phase. The sexual arousal stimulates the neurotransmitter nitric oxide (NO) which regulate the formation of cGMP that relaxes the smooth muscles and blood flow to the penis (Moreland et al. 2001). 3. Definition of erectile dysfunction and its prevalence: The National Institute of Health (NIH) in 1993 defined Erectile Dysfunction as the persistent inability of a man to achieve and maintain an erection sufficient for a satisfactory sexual performance (NIH Consensus Impotence 1993). The prevalence of erectile dysfunction is increasing according to a study conducted in Massachusetts Male Aging Study (Feldman et al. 1994) found an ED prevalence of 52 % in 40 – 70- year-old men. While another study conducted in Germany shows the result no more different then earlier study In the German “Cologne Male Survey” (Braun et al. 2000), a significant age-correlated increase of 10% in the incidence of ED was found in men between the ages of 40 and 49, 16% in men between 50 and 59, 34% in men between 60 and 69, and over 50% in men between 70 and 80 years of age. 4. Therapeutic treatment for Erectile dysfunction: Before the discovery of PGE-5 drugs the doctor directly go for the penis implantations which is now hardly used as the treatment. The other drug treatment includes inra-cavernosal or intreurethral injections of vasoactive substances. These treatments were very unpleasant for the patients. There are many other drug treatment approaches with different level of efficacy like the treatment with synthetic prostaglandin analogue ( PGE-1) this treatment prolongs the erection by increasing the cAMP level in the corpus carvenosum (Andersson 2001). Phosphodiesterases: There are about 21 different sub-groups of PDE. As these are involved in essential bodily functions, a question is raied here whether the PDE-5 inhibitor also inhibit other phosphodiesterases. These inhibitors are mai