An event monitor is a small electronic device that helps your doctor diagnose arrhythmias (ah-RITH-me-ahs), or problems with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. An event monitor can be used if an EKG or Holter monitor can’t diagnose the arrhythmia, usually because the symptom is very infrequent and can’t be “caught” during the few moments of an EKG or even the one or two days of a Holter monitor. There are two types of these monitors – one can be kept in the pocket until you feel your symptom, when you then touch it to your skin and record your heart, and the other (helpful for infrequent, but very short symptoms) is worn attached by wires to your body. Both of these devices are typically used for up to 30 days. While inconvenient (but not painful or invasive), they are very important tests that may help your doctor diagnose your condition.