Delivery of an implantable wireless receiver-stimulator (R-S) into the heart using delivery catheter is described. R-S comprises a cathode and an anode and wirelessly receives and converts energy, such as acoustic ultrasound energy, to electrical energy to stimulate the heart. Conductive wires routed through the delivery system temporarily connect R-S electrodes to external monitor and pacing controller. R-S comprises a first temporary electrical connection from the catheter to the cathode, and a second temporary electrical connection from the catheter to the anode. Temporary electrical connections allow external monitoring of heart's electrical activity as sensed by R-S electrodes to determine tissue viability for excitation as well as to assess energy conversion efficiency.