When a pacemaker over-senses there may be a lower than preset heart rate, possible palpitations (rapid heartbeat, often accompanied by panic), chest tightness, and heart palpitations. Oversensing occurs when the pacemaker incorrectly senses non-cardiac electrical activity and is prohibited from pacing.This form of output failure may be due to muscle activity (especially the diaphragm or chest muscles), electromagnetic interference (EMI) (from magnetic resonance imaging [MRI]), or a break in the insulation of the leads. This may cause the heart rate to fall below the preset heart rate, or, in some patients who cannot tolerate it, palpitations (rapid heartbeat, often accompanied by panic), chest tightness, and dizziness. Oversensing is a diagnostic and therapeutic condition that can be diagnosed and treated with the use of magnets. After pacemaker implantation, it is important to have regular follow-ups in the hospital and to have the device regulated under the guidance of the clinician.