What is an electrocardiogram?
An electrocardiogram (ECG) is one of the simplest and fastest tests used to evaluate
the heart. Electrodes (small, plastic patches that stick to the skin) are placed at
certain spots on the chest, arms, and legs. The electrodes are connected to an ECG
machine by lead wires. The electrical activity of the heart is then measured, interpreted,
and printed out. No electricity is sent into the body.
Natural electrical impulses coordinate contractions of the different parts of the
heart to keep blood flowing the way it should. An ECG records these impulses to show
how fast the heart is beating, the rhythm of the heart beats (steady or irregular),
and the strength and timing of the electrical impulses as they move through the different
parts of the heart. Changes in an ECG can be a sign of many heart-related conditions.
Why might I need an electrocardiogram?
Some reasons for your doctor to request an electrocardiogram (ECG) include:
To look for the cause of chest pain
To evaluate problems which may be heart-related, such as severe tiredness, shortness
of breath, dizziness, or fainting
To identify irregular heartbeats
To help determine the overall health of the heart before procedures such as surgery;
or after treatment for conditions such as a heart attack (myocardial infarction, or
MI), endocarditis (inflammation or infection of one or more of the heart valves);
or after heart surgery or cardiac catheterization
To see how an implanted pacemaker is working
To determine how well certain heart medicines are working
To get a baseline tracing of the heart's function during a physical exam; this may
be used as a comparison with future ECGs, to determine if there have been any changes
There may be other reasons for your doctor to recommend an ECG.
What are the risks of an electrocardiogram?
An electrocardiogram (ECG) is a quick, easy way to assess the heart’s function. Risks
associated with ECG are minimal and rare.
You will not feel anything during the ECG, but it may be uncomfortable when the sticky
electrodes are taken off. If the electrode patches are left on too long they may cause
There may be other risks depending on your specific medical condition. Be sure to
discuss any concerns with your doctor before the test.
Certain factors or conditions may interfere with or affect the results of the ECG.
Anatomical considerations, such as the size of the chest and the location of the heart
within the chest
Movement during the test
Exercise or smoking before the test
Electrolyte imbalances, such as too much or too little potassium, magnesium, or calcium
in the blood
How do I get ready for an electrocardiogram?
Your doctor or the technician will explain the test to you and let you ask questions.
Generally, fasting (not eating) is not required before the test.
Tell your doctor of all medicines (prescribed and over-the-counter), vitamins, herbs,
and supplements that you are taking.
Tell your doctor if you have a pacemaker.
Based on your medical condition, your doctor may request other specific preparation.
What happens during an electrocardiogram?
An electrocardiogram (ECG) may be done on an outpatient basis or as part of your hospital
stay. Steps may vary depending on your condition and your doctor’s practices.
Generally, an ECG follows this process:
You will be asked to remove any jewelry or other objects that may interfere with the
You will be asked to remove clothing from the waist up. The technician will ensure
your privacy by covering you with a sheet or gown and exposing only the necessary
You will lie flat on a table or bed for the test. It will be important for you to
lie still and not talk during the ECG, so that you don’t alter the tracing.
If your chest, arms, or legs are very hairy, the technician may shave or clip small
patches of hair, as needed, so that the electrodes will stick closely to the skin.
Electrodes will be attached to your chest, arms, and legs.
The lead wires will be attached to the electrodes.
Once the leads are attached, the technician may enter identifying information about
you into the machine's computer.
The ECG will be started. It will take only a short time for the tracing to be completed.
Once the tracing is completed, the technician will disconnect the leads and remove
the skin electrodes.
What happens after an electrocardiogram?
You should be able to go back to your normal diet and activities, unless your doctor
tells you differently.
Generally, there is no special care after an electrocardiogram (ECG).
Tell your doctor if you develop any signs or symptoms you had before the ECG (for
example, chest pain, shortness of breath, dizziness, or fainting).
Your doctor may give you other instructions after the test, depending on your particular
Before you agree to the test or the procedure make sure you know:
The name of the test or procedure
The reason you are having the test or procedure
What results to expect and what they mean
The risks and benefits of the test or procedure
What the possible side effects or complications are
When and where you are to have the test or procedure
Who will do the test or procedure and what that person’s qualifications are
What would happen if you did not have the test or procedure
Any alternative tests or procedures to think about
When and how you will get the results
Who to call after the test or procedure if you have questions or problems
How much you will have to pay for the test or procedure