How to read an ECG graph

Comstock/Comstock/Getty Images

An ECG – electrocardiogram – is a medical test that measures the electrical activity and rhythm of the heart. A doctor applies small electrodes to the patient’s chest, legs and arms. The electrodes connect to an ECG machine that records the electrical signals associated with the patient’s heart beat.

The machine produces a printout of the heart’s rhythm on graph paper. Although diagnosing a heart condition is best left to medical experts with years of training and experience, you can read an ECG printout to find out your heart rate.

Ask your doctor or nurse if you can see the printout of your ECG results. Most medical professionals will be happy to provide this information. It also gives them an opportunity to talk to you about the results and any action that might be necessary.

Look at the ECG printout. This will show a horizontal wave form line running across a grid pattern from left to right. Each 1 mm grid square on the horizontal axis represents duration of 0.04 seconds. Each 5 mm grid square represents 0.2 seconds. The heart’s electrical activity is measured on the vertical axis, with each 10 mm grid square equivalent to 1mV in voltage.

Study the vertical “blips” in the wave form. The blip is known as a QRS complex and each one represents a beat of the heart. You can now work out your heart rate from the information on the ECG chart.

Divide the figure of 300, representing a regular heart rhythm, by the number of 5 mm grid squares between each QRS complex on the horizontal axis. For example, if four grid squares appear between each QRS complex, your heart rate is 300 divided by four, which is 75. Follow the next step if your heartbeat is irregular.

Count the number of R waves – the R wave is the highest point of the QRS complex wave form – in a six second strip. Multiply this figure by 10. For example, seven R waves mean seven multiplied by 10, which gives a heart rate of 70.