Heat transfer enhancement by pulsating flow in a triangular grooved channel has been experimentally investigated for the ranges of 270 <= Re <= 910 and 0.08 <= St <= 0.67. It is measured that the heat transfer improved up to 350% at Re = 270 and St = 0.34 compared with the steady flow case. The heat transfer enhancement is found to increase as Reynolds number decreases. It is also found that the optimal Strouhal number increases as Reynolds number decreases. To analyze the correlation between the pulsating flow behaviors and the heat transfer enhancement characteristics, a PIV investigation has been performed. The PIV results show that the heat transfer, enhancement results from the strong mixing caused by the repeating sequence of vortex generation, growth, expansion and ejection from the groove to the main stream by the pulsating flow. The fluid mixing enhancement is maximized when the pulsation period matches with the time duration for the vortex to grow large enough to fill the groove and then to be ejected to the main stream. (C) 2007 Published by Elsevier Ltd.