The dependence of the Nusselt number in the separated flow behind a circular cylinder to the cross-flow varies greatly with Reynolds number according to the flow regimes, i.e., laminar shedding, wake transition, and shear-layer transition regimes. The Nusselt number at the rear stagnation point, Nu(r)/Re-0.5, increases with Reynolds number in the laminar shedding regime (Re < 150) and the shear-layer transition regime (3000 < Re < 15 000), corresponding to the shortening of the vortex formation region. On the contrary, the Nusselt number, Nu(r)/Re-0.5, decreases with Reynolds number in the regime in which the wake develops to a complex three-dimensional flow (300 < Re < 1500), corresponding to the lengthening of the vortex formation region. This distinctive change affects the correlation of the overall Nusselt number with Reynolds number, i.e., the exponent of the Reynolds number has a lower value for 200 < Re < 2000 than that for 70 < Re < 200 and Re > 2000. (C) 2004 Elsevier Ltd. All rights reserved.