A single pass medical electrical lead featuring an atrial wall wedging mechanism which will permit the atrial electrodes to be positioned directly against the right atrial wall. In the preferred embodiment the atrial wall wedging mechanism comprises an extendible finger which may be used to wedge the lead body in the region where the inferior vena cava enters the right atrium and the right atrium empties through the tricuspid valve into the right ventricle. Through such wedging, the atrial electrodes may be caused to be positioned directly against the right atrium wall without causing excessive pressure to be communicated to the distal tip of the lead.