Seasonal heat transport in the North Pacifc and North Atlantic Oceans is compared using a 49-year long analysis based on Simple Ocean Data Assimilation of Carton et al.( 2000). In midlatitudes surface heat flux is largely balanced by seasonal storage, while equatorward of 15N, divergence of heat transport balances seasonal storage. The seasonal cycle of heat transport in the Pacific is in phase with the annual migration of solar rediation, transporting heat from the warm hemisphere to the cool hemisphere. Analysis shows that the cycle is large with peak-to -peak shifts of 5PW. Important contributions are found from the annual cycle of wind drift in the mixed layer and adiabatically compensating return flow. The annual cycle of heat transport in the North Atlantic is also large. Here too, wind-driven transports play a role, although not as strongly as in the pacific, and this is an important reason for the differencies in heat transport between the basins.