Although percussion guns are not on the official list of devices that can alter the functioning of pacemakers, it is important that you consult a doctor about whether or not it is advisable to use them in your particular case.
Pacemakers are usually installed under the collarbone and in the abdomen, so constant stimulation with pressure may slightly alter their function. When in doubt about how to use the gun, it is best to have all available guidance before the gun.