ECG stands for electrocardiogram, a simple non-invasive test that tells us about what your heart is doing. 
Your heart generates a little electrical impulse to create every single heartbeat. These impulses flow through the heart from the top chambers (atria) through to the bottom pumping chambers (ventricles). Since this happens with each heart beat, in most people this is around 60 times per minute to 100 timues per minute, and faster when you exercise.

The ECG lets us break down each component of your heartbeat – the part where your atria squeeze, the part where your ventricles squeeze, and the part where the ventricles relax. By separating these parts, we can see if there is an electrical problem with each of these parts. Remember, it only shows us the electrical signal, so any mechanical problem, like the artery have a narrowing or the muscle being weak doesn’t get seen (although we can get some clues).

These electrical impulses can be picked up using an ECG machine (electrocardiograph). Nine small patches are placed in various places around your body – six on your chest, one near each shoulder, and one on your lower abdomen or foot. There are specific patches available for people who have allergies. Each of these provides a different signal, and together we can use them to assess different regions of the heart.

What can an ECG tell us?

• your heart rate (are you bradycardic or tachycardic?)
• your heart rhythm (is it regular or irregular, like in an arrhythmia?)
• signs of a previous heart attack
• signs of a current heart attack (if you are having symptoms)
• signs of ischaemia, a reduced blood supply to the heart (usually not seen at rest; often exercise is used while recording an ECG, called a stress ECG)
• signs of a cardiomyopathy (an abnormality in your heart muscle)

The test is quick (less than five minutes) and involves no needles or radiation. The result is printed instantly at the bedside. The ECG machine attempts to do some interpretation and tell you the result, but this is fraught with inaccuracy and should be interpreted by an experienced professional.

In some other countries, this test is called an EKG, for electrokardiograph.