A leadless pacing device may include a housing having a proximal end and a distal end, and one or more electrodes supported by the housing. The housing may include a body portion and a header. A distal extension may extend distally from the header of the housing, the distal extension including one or more electrodes. The header may include a guide wire port and a guide wire lumen may extend from the guide wire port through the header of the housing and through the distal extension. A fixation member may extend from the header of the housing. The header may be formed from an over mold process.