Arrhythmias can be detected by an electrocardiogram, which shows the pattern of electrical activity within the heart muscle. A device called a Holter monitor can also be used. This device records all heartbeats within a 24-hour period.
More complicated arrhythmias can be identified by a cardiac catheterization. In this procedure, a doctor inserts a catheter into the heart through a vein in the leg. The electrical impulses of the heart can then be measured to determine exactly what type of arrhythmia is present.