Listening to the heart with a stethoscope shows an irregular rhythm. The pulse may feel rapid, irregular, or both. Sometimes the pulse is too slow. The normal heart rate is 60 to 100, but in atrial fibrillation/flutter the heart rate may be 100 to 175 may be normal or low.
An Electrocardiogram (ECG) which measures the rate and regularity of heartbeats as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart will help identify atrial fibrillation or atrial flutter. Continuous ambulatory cardiac monitoring -- Holter monitor (24 hour test) -- may be necessary because the condition is often sporadic (occurring at some times but not others).