Inclusion Criteria:  Pediatric patients with tetralogy of Fallot spectrum. Sex (males and females) Age 6 months- 5 years.  Exclusion Criteria:  Persistent left SVC draining in the coronary sinus. Mental or neurologic disorders. Preoperative critically ill patients. Parents or legal guardian refusal. Fallot repair with transannular patch( as it will affect on the RV function as a single agent after reperfusion)