The present invention relates to a catheter suitable for conducting and positioning a medical device in an organic cavity comprising at least one side branch, such as a blood vessel, which comprises a tubular body, having a central lumen having a cross-section suitable for the passage of the medical device and a mandrel slidable in the central lumen and distally a flexible end portion. On the outer surface of the mandrel there is a longitudinal groove defining, with the inner wall of the tubular body, a passage suitable for receiving a first guide wire in a sliding manner. In addition, in the mandrel there is an inner lumen suitable for housing a second guide wire in a sliding manner. The present invention further relates to a catheter assembly comprising the aforesaid catheter and a method of use the same.