It is known that inside a cylindrical cavity placed at the way of an underexpanded jet, pressure oscillations accompanied by heat release can be excited. In spite of many works conducted in the past, some questions still remain about the heating mechanism, mainly due to the experimental difficulties associated with the flow structure of an underexpanded jet. The experimental results presented in this paper show that a drastic heating takes place when a cavity, filled by jet, exhibits cyclical oscillations of pressure, where the minimum cavity pressure corresponds to the level of ambient pressure outside the cavity. (C) 2003 Elsevier Science Ltd. All rights reserved.