Background : Progress in reproductive technology has shown that nitric oxide (NO) is involved in fertilization process and is found in the follicle as well as the sperm, decidualization and implantation. Endometrial growth is thought to depend on uterine artery blood flow and the importance of endometrial development on in-vitro fertilization (IVF) outcome has been previously reported. Sildenafil citrate (Viagra) is a type 5-specific PDE inhibitor that prevents the breakdown of cGMP and potentiates the effect of NO on vascular smooth muscle. Patient and methods : This is a prospective randomized controlled study. Fifteen cases will be given sildenafil citrate with IVF preparatory protocol and the other Fifteen cases will be used as a control cases (they will be given IVF induction protocol without sildenafil). Inclusion and exclusion were set. Conclusion : The notion of increasing pregnancy rate among women undergoing ICSI is still far from reality. Among factors affecting implantation rate and pregnancy rate, endometrial thickness remain poorly understood.The use of vaginal sildenafil showed no significant increase in endometrial thickness in cases undergoing ICSI. Yet metaphase ΙΙ, cleaved embryos, number of embryo transfer/cycle and finally implantation rate increased which may be due to improvement of endometrial and ovarian microvascular circulation or decrease NK activity. More controlled randomized trials with large sample size are needed to address these issues.