A cardiac rhythm management system includes a lead assembly for intracardiac mapping, pacing, and drug delivery. The lead assembly includes an implantable endocardial lead having a proximal end for connection to an implantable cardiac rhythm management device and a distal end for disposal in an intracardiac region. The lead includes a pacing-sensing electrode and a drug delivery device, both located at or near the distal end. A lumen is within and extends throughout the lead, with an opening at or near the proximal end and another opening at or near the distal end. The lumen provides for access to the intracardiac region by a steerable stylet and a hollow needle, one at a time. The steerable stylet allows for electrophysiological mapping of the intracardiac region. The hollow needle allows for delivery of chemical, biochemical, and/or biological substance to the intracardiac region.