Observations show that the upper ocean has been warming since the 1970s, and it is usually attributed to global warming that is associated with the increasing concentration of greenhouse gases in the atmosphere. The global ocean is implicitly considered as a passive heat reservoir, and it is assumed that the ocean was in equilibrium with the atmosphere before the anthropogenic global warming had occurred. However, the global ocean is a dynamically active heat exchanger involving processes of various temporal and spatial scales and has a memory of thousands of years. Not only the heat exchange between ocean and atmosphere but the vertical heat flux passing the lower face of the upper ocean (the vertical redistribution of heat) contribute to the changes in the observed upper ocean heat content. In this talk, I will present the mean and the bidecadal change of the ocean vertical heat flux as well as the related physical processes from a dynamically consistent and data-constrained ocean state estimate – ECCO (Estimating the Circulation & Climate of the Ocean). Implications of the vertical redistribution of ocean heat on the changes of the upper and deep ocean heat contents, particularly the recently much-debated global warming “hiatus”, will also be discussed.