A catheter adapted to perform electrophysiological procedures comprises a body member, a manipulation handle attached to the proximal end of the body member for applying torque to the body member, the handle having a control knob adapted for control movements in a first plane and in a second plane simultaneously. A deflection control line is attached at its distal end to the distal portion of the catheter and its proximal end attached to the control device of the handle so that tension applied to the control line by sliding the control knob causes deflection of the distal portion of the catheter. A stiffening member is disposed within the body member of the catheter and is slidable, said stiffening member providing increased rigidity to the portion of the body member in which the stiffening member is located. Rotation of the control knob controls the position of the stiffening member in the body member. In a further aspect, a stiffening member in accordance with one embodiment includes a tapered distal end section with a ball formed on the distal tip, the tapered section terminating at the ball. In accordance with another aspect, the torsional rigidity of the catheter body is increased by use of a layer of aramid fibers mixed with an epoxy. In yet another feature, the handle and rotatable sliding element are symmetrically shaped to facilitate complete single-handed operation of the handle by the physician of all position control aspects of the catheter.