Electrocardiogram (ECG). During an ECG, sensors (electrodes) that can detect the electrical activity of

your heart are attached to your chest and sometimes to your limbs. An ECG measures the timing and

duration of each electrical phase in your heartbeat.

Holter monitor. This portable ECG device can be worn for a day or more to record your heart's activity

as you go about your routine.

Event monitor. For sporadic arrhythmias, you keep this portable ECG device at home, attaching it to

your body and using it only when you have symptoms of an arrhythmia. This lets your doctor check your

heart rhythm at the time of your symptoms.

Echocardiogram. In this noninvasive test, a hand-held device (transducer) placed on your chest uses

sound waves to produce images of your heart's size, structure and motion.

Cardiac computerized tomography (CT) or magnetic resonance imaging (MRI). Although more

commonly used to check for heart failure, these tests can be used to diagnose heart problems that might

cause heart arrhythmias. In a cardiac CT scan, you lie on a table inside a doughnut-shaped machine. An

X-ray tube inside the machine rotates around your body and collects images of your heart and chest.

In a cardiac MRI, you lie on a table inside a long tube-like machine that produces a magnetic field. The

magnetic field aligns atomic particles in some of your cells. When radio waves are broadcast toward

these aligned particles, they produce signals that vary according to the type of tissue they are. The

signals create images of your heart that can help your doctor determine the cause of your heart

arrhythmia.