An implantable electrical lead for electrical sensing and stimulation of the heart includes a lead body which includes a ventricular tip, a pair of distal atrial ring electrodes, a pair of proximal atrial ring electrodes, a pair of first stationary contacts in electrical continuity, respectively, with the distal atrial ring electrodes, and a pair of second stationary contacts in electrical continuity, respectively, with the proximal atrial ring electrodes. A bifurcation boot overlies the lead and is slidable lengthwise of the lead body. The bifurcation boot carries first and second mobile contacts movable between first and second longitudinally spaced positions on the lead body. In the first position, the first and second mobile contacts are engaged with the first pair of the stationary contacts, respectively. In the second position, the first and second mobile contacts are engaged with the second pair of the stationary contacts, respectively. Stop members integral with the lead body and engaged by the bifurcation boot establish the first and second positions.