context: If your heart seems to skip a beat, race, or work a bit too slow, you could have a condition known as arrhythmia. Your doctor might suggest you wear a device called a Holter monitor. This simple at-home tool helps track your heart's rhythm around the clock for a few days while you work, sleep, play, and do everyday tasks. Your doctor may refer to the device as an "ambulatory electrocardiogram," or ECG. That sounds a little scary, but ambulatory just means walking or moving around. It applies to the monitor, which you can wear or carry with you. An ECG is a test that measures the movement of electrical signals or waves through your heart. These signals tell your heart to contract (squeeze) and pump blood. Sometimes they aren't working right, and the irregular rhythm that results can lead to heart attack or stroke. The monitor helps your doctor figure out what's going on in your ticker before it becomes a bigger problem. This battery-operated device is about the size of a postcard or digital camera. It continuously records your heart's electrical activity for at least 24 to 48 hours. Some newer models can record for up to 2 weeks. Tiny wires connect the monitor to patches called electrodes that go on your chest. If you have a lot of chest hair, a technician may need to shave some off so the electrodes can stick firmly to your skin. Sometimes the patches can fall off, so you might need extra tape. You can wear the monitor over your shoulder like a purse, around your neck like a camera, or attached to your belt. Or you can carry it with you in a pocket. You won't take it off during the test period unless you're in the bath or a pool. Once the monitor is in place, you'll be told how to: Take care of it and change the batteries if needed Push a button on the monitor if you feel any heart symptoms Keep a written diary of all symptoms, including chest pain, changes in heartbeat, and dizziness, when they occurred, and what you were doing at the time After the test period, you'll go back to see your doctor. He'll download the information. It's important to note that Holter monitors don't give real-time results. It may take a week or two to get them. Your doctor will compare the recorded results to your written symptom diary to help diagnose or rule out any heart problems. Reasons your doctor might recommend a Holter monitor include: You have a fast, pounding, or fluttering heartbeat. Your heartbeat is too slow, too fast, or otherwise irregular. You're tired, short of breath, dizzy or feeling faint. You have chest pain that isn't caused by an exercise test. There's a need to know how well your heart medication or pacemaker is working. The doctor needs to determine if you are at risk for future heart problems after a heart attack or because of another genetic or pre-existing condition. You have a pacemaker and feel dizzy. A monitor can help diagnose many heart conditions, including: Atrial fibrillation, a rapid heartbeat that can lead to stroke Ventricular tachycardia, a fast heartbeat that starts in your heart's lower chambers Other irregular heartbeats (your doctor might call them "cardiac arrhythmias"), including signaling (conduction) disorders and slow heartbeat A Holter monitor is painless. There are no risks. However, some people have mild skin irritation from the tape used to attach the electrodes to the chest. The heart test is relatively inexpensive compared to real-time, continuous heart monitoring. One drawback is that you can't get the monitor wet, so you can't bathe, shower, or swim. Taking it off for one of those things isn't a good option. You might miss an important heart event that could give your doctor key information about your health. If your doctor recommends this test for you, you need to keep the monitor on during the entire test period. You'll also need to write in your symptom diary and push the monitor's event button if you feel symptoms of a heart problem. If you don't, the monitor won't provide useful information. Other things around the house can affect your results. Keep your monitor at least 6 inches away from mobile phones and stay away from MP3 players. Some other things that scramble the device include: Magnets, metal detectors, and high-voltage electrical wires Microwaves Electric razors and toothbrushes Smoking and tobacco use Certain medications If you have chest pain that doesn't go away after a few minutes or other symptoms of a heart attack while wearing a Holter monitor, don't try to wait to get help until you go to your doctor. You need to get emergency medical help or call 911 right away.