An intravenous lead assembly for atriolventricular (AV) sequential pacing includes a channel and a separable core lead. The channel lead and the core lead respectively include first and second helical coil conductors through which first and second wire stylets can be inserted. The first and second helical coil conductors are embedded in first and second elongated silicone rubber sleeves, respectively. The silicone rubber sleeve of the channel lead includes an elongated channel. In use, the core lead is passed through the channel of the channel lead either before or after the channel lead is passed through selected veins into a patient's heart. Handles are provided on the proximal ends of the stylets to enable a physician to manipulate the distal ends of the channel lead and core lead. In one embodiment of the invention, the channel terminates in a side port of the channel lead, enabling the physician to guide the top of the core lead out of the side port and into the right ventricle after the distal end of the channel lead has been positioned in the coronary sinus or the right atrial appendage.