Abstract: A heat exchanger for vehicles comprises firstly a heat-exchanger assembly consisting of flat liquid-conveying tubes and surface-enlarging means, secondly an inlet tank, and thirdly an outlet tank. The inlet tank and the outlet tank have a connection plate with a number of connection holes for the tubes. At each hole, the plate has a projecting connecting sleeve element. Each tube has at its ends a widened main portion which is accommodated on said connecting sleeve element. A rounded transitional area is formed between the connection plate and each connecting sleeve element, and the main portion is inserted in the conecting sleeve element and is applied with its outside against the inside of the connecting sleeve element. Each tube has at its ends an end portion which is widened in relation to the main portion, merges with the main portion and is applied against the transitional area.