We propose to investigate the high frequency dynamics of ionic liquid (IL), 1octyl-3-methylimidazolium chloride ([C8MIM]Cl) deuterated by means of Inelastic Neutron Scattering (INS) in the mesoscopic regime as a function of temperature, from below the glass transition up to well inside the neat liquid regime. Aim of the experiment is to characterize, for the first time, collective dynamics in the mesoscopic regime for ILs, and investigate the relation between structural and dynamical heterogeneities. This study will shed light on the relationship between structural relaxations and transport properties of ionic liquids, a key property in many applications.