The propagation behaviour of an initial thermal perturbation in liquid argon is simulated by the molecular dynamics method. The 12-6 Lennard-Jones potential and mirror boundary conditions are employed in the 32768-particle three-dimensional simulation. Macroscopic characteristics such as the kinetic temperature, pressure and momentum profiles are monitored during the simulation in order to examine the heat propagation behaviour under a timescale comparable with the relaxation time. The results show that the behaviour is still diffusion-like; no features predicted by the Cattaneo-Vernotte model have been found. The wave-like front of the local temperature may be caused by the adiabatic compression and expansion by the pressure wave generated by the thermal expansion. PACS:  44. 10. +i, 02. 70. Ns, 61. 25. Bi