Heat transfer in turbulent forced convection of power-law fluids, in a heated horizontal pipe at isoflux conditions, is analyzed by large eddy simulations (LES), with an extended Smagorinsky model. A temperature dependent fluid is studied at various Pearson numbers (0 ≤ Pn ≤ 5), for two power law indices (n = 0.75 and 1), at Reynolds and Prandtl numbers Re=4000 and Pr=1. The LES predictions are validated through comparisons with the literature at Pn=0. They allow a better understanding of the physical mechanisms involved in the non-Newtonian temperature dependent fluid flows: with increasing Pn, the relative viscosity is reduced close to the wall and enhanced towards the pipe center, reducing the turbulent fluctuations and heat transfer in the bulk and, as a consequence, the friction factor and Nusselt number.