Heat transfer in transitional curved channel flow is investigated over a range of Dean numbers less than 300. The channel aspect ratio is 40, radius ratio is 0.979 and the ratio of boundary layer thickness to channel width is 0.011. Forced convection Nusselt numbers show the influences of Dean vortex pairs and other transitional phenomena. In particular, Nusselt numbers on the concave surface become higher than ones measured at the same streamwise location on the convex surface just after the start of curvature. Important Nusselt number increases also occur due to the twisting secondary instability as the Dean number increases from 150 to 200.