Spatially-resolved Nusselt numbers and flow structural characteristics are presented for a stationary channel with an aspect ratio of 8 and a staggered array of pin fins between two of the surfaces. Local Nusselt numbers, measured on one endwall, are highest beneath primary and secondary horseshoe vortices located just upstream of individual pins, beneath pin wakes, and downstream of the pins, in regions where shear layers are positioned between the wakes behind the pins and the higher speed flow away from an individual pin. Also important are intense, highly unsteady secondary flows and vortex pairs (evident in flow visualizations and time-averaged surveys), which increase secondary advection and turbulent transport over the entire channel cross-section. (C) 2003 Elsevier Ltd. All rights reserved.