The physical origin of the well-known maximum occurring in the dynamic heat storage capacity of a harmonically excited slab is analysed in terms of the fundamental solutions of Fourier＇s equation. It is shown that, in addition to this maximum, an infinite sequence of exponentially decaying lateral minima and maxima occur which are generated by a coherent superposition of two thermal waves propagating in opposite directions within the slab. By passing from the parabolic to the hyperbolic description of heat conduction, this effect becomes much more pronounced.