Abstract: A heat exchanger, especially a heating heat exchanger in the engine cooling circuit of a motor vehicle is disclosed. A forward-flow pipe opens at the top into a water box. A vent line of small cross-section is assigned to the forward-flow pipe and is guided to a compensating tank and there terminates below the liquid level. In order to obtain a simply constructed and at the same time highly effective venting facility, the vent line is brought into the operative position together with the fastening of the forward-flow pipe and is guided away from the highest point of the forward-flow water box to the compensating tank located at a distance therefrom.