Abstract: An infusion apparatus comprising an indwelling venous cannula with a catheter holder, a plastic catheter and a steel cannula holder with a steel cannula extending through the plastic catheter and the catheter holder, a tubular valve body made of elastomeric plastic with certain length L being disposed in a channel extending centrally through the housing of the catheter holder, and the walls of the valve body lying on and directly touching each other over certain length L, whereby certain length L, the wall thickness and the Shore hardness of the valve body are coordinated with each other so that an infusion solution can pass the valve under the effect of gravity but a reflux of the patient's blood is reliably prevented. The valve body is preferably a tubular film.