The atrial septum provides a convenient structure to which a transvenous electrode can be attached securely. The Brokenbrough cardiac catheterization technique has been used to gain access to the left atrium. A new electrode has been fabricated which can be inserted into the left atrium through the lumen of a Brockenbrough catheter. The electrode is composed of a stainless steel coil attached inside the proximal end of a platinum cylinder at the cardiac terminal. Three Elgiloy wires, having a wing configuration, are attached inside the distal end of the platinum cylinder. The coil and cylinder are insulated by silicone rubber and the metallic surface area of the distal electrode tip equals 5 mm2. This electrode has been implanted without difficulty or complications in five patients with tachycardia-bradycardia syndrome.