Introduction: Determination of mean flow velocity (MFV) in the middle cerebral artery (MCA) by transcranial Doppler (TCD) may allow early detection of alteration in cerebral hemodynamics during and after cardiac surgery in infants. Methods:In 55 neonates and infants with cyanotic and non-cynotic congenital heart disease (CHD) below the age of 9 monthes (weight 7.5±4 kg) undergoing surgical correction by means of full flow CPB (120-150 ml/Kg/BW) with moderate hypothermia (24+6 C°) and alpha-stat strategy were included in this study. Continuous TCD (Multi-Dop P, DWL) monitoring allowed on-line recording MFV and the pulsatility index(PI=maximal flow velocity - enddiastolic flow velocity/mean flow velocity).Results: The nonpulsatile cerebral flow during CPB resulted in lower calculated PI as well as a gradual decrease of MFV in all infants(p<0.001). After the end of CPB an initially decreased diastolic flow velocity pattern - resulting in higher calculated PI and lower MFV - was normalized at the end of operation. The postbypass Vm values correlated significantly to weight (r=0.78, p<0.0001), bypass-time (r=0.60, p=0,006) and minimal rectal temperature (r=0.63, p=0,003).Conclusion: the increase of PI after the termination of CPB may indicate transient increase in cerebrovascular resistance. Whether the alteration in cerebral hemodynamics is related to possible occured cerebral injury requires further studies.