Methods of threshold testing and setting a voltage on an artificial pacemaker based on the output of a plethymograph, such as an oximeter, are disclosed herein. This is accomplished by determining blood volume in a limb or area of the body, and its change over time. As voltage is decreased in the pacemaker, a change in blood volume of the limb being measured by the oximeter is determined. This change can be a change in how often the blood volume level rises to its peak level and/or the blood volume level no longer rises substantially. Such changes, or lack thereof, can be based on a backup heart rate or no heart rate at all. Once the threshold voltage is determined where the artificial pacemaker ceases to cause a heartbeat, the voltage of the pacemaker can be set accordingly.
