Arrhythmia is any variation from the normal rhythm of the heartbeat. The heart rate at rest is usually between 60 and 100 beats per minute. Much lower rates may be normal in young adults, particularly those who are physically fit. Some variations in heart rate are normal. The heart rate responds not only to exercise and inactivity but also to such factors as pain, anger, anxiety and stress.

Only when the heart rate is too fast or too slow or when the electrical impulses travel in abnormal pathways is the heartbeat considered abnormal. Such rhythms may be regular or irregular.

A patient's description of symptoms often helps the doctor diagnose an arrhythmia and determine how serious it is. The most important considerations are whether:

• The heartbeats are fast or slow, regular or irregular, or short or long
• The person feels dizzy, light-headed or faint or even loses consciousness
• The person is experiencing chest pain, shortness of breath or other unusual sensations, along with the palpitations
• The palpitations happen when the patient is at rest or only during strenuous or unusual activity
• The palpitations start and stop suddenly or gradually

Techniques for finding the exact nature of arrhythmia include:

• Electrocardiography (EKG) is the main technique for detecting arrhythmias. This test can provide a picture of the arrhythmia. An EKG shows the heart rhythm over a brief time. Often, however, arrhythmias come and go.
• A portable monitor (Holter monitor) that the patient wears for 24 hours or extended periods of time can record arrhythmias that may occur during a normal day. The patient is also asked to keep a diary of symptoms while the monitor is worn.
• Electrophysiologic studies may be helpful when long-term, life-threatening arrhythmia is suspected. A tube containing wires is threaded through a vein into the heart. An electrical impulse is sent to the heart that shows up on a computer screen. Most serious heart rhythm abnormalities can be detected this way. The test data allow the doctor to identify the type of arrhythmia and the best treatment for it.