On the basis of an endoreversible Carnot heat-engine model, the frequency-dependent performance of the engine is analyzed when the heat transfers between the working fluid and the heat reservoirs obey a linear phenomenological heat-transfer law, i.e., Q proportional to (Delta T-1). The relations among average power-output, efficiency, available temperature-drop, cycle frequency and ratio of the heat-transfer times are derived. They are different from those obtained with Newton's law. The results can provide guidance for selecting the appropriate working points of heat engines. (c) 2004 Elsevier Ltd. All rights reserved.