Using the method of molecular dynamics, we have examined the decay of an instantaneously imposed heat pulse on an equilibrium model fluid similar to super-critical argon, The spatial extent of the initial pulse is quite small - on the order of 100 nm(3); the amount of energy added to the system is only 5% of the total system kinetic energy. This small pulse decays quite rapidly, within several picoseconds, but the decay proceeds more slowly than predictions based on the hydrodynamic equations. During the first picosecond of the decay, the kinetic energy is not equipartitioned and a very fast process of energy transfer from kinetic energy to potential energy takes place. A good fit to the molecular dynamics data is obtained using a simple linear superposition of the hydrodynamic and free streaming theories.