Fentanyl is a highly selective mu-agonist (or MOP agonist); the MOP receptor appears to be specifically involved in the mediation of analgesia. Opioids appear to exert their effects by interacting with presynaptic Gi-protein receptors, leading to hyperpolarization of the cell membrane by increasing K+ conductance. Inhibition of adenylate cyclase, leading to reduced production of cAMP, and closure of voltage-sensitive calcium channels also occur. After institutional scientific and ethical committee approval, a written informed consent was obtained from parents. 70 paediatric patients, American Society of Anesthesiologists (ASA) physical status II and III, aged between 4 to 12 yrs with acyanotic congenital heart disease admitted for elective interventional cardiac catheterization procedures are included in this study. There is significant difference in the mean duration of sedation attained by group D and group F both statistically and clinically. The sedation time does include the procedure duration and duration from end of procedure to attainment of the steward score of 7.