Palpitations
Fast or irregular heartbeats, a heart that “skips” a beat, particularly strong heartbeats or a fluttering sensation in the chest.
The ECG shows the heart rhythm present at the time of the recording.
Diagnostic tests · Saint‑Hyacinthe12-lead ECG
Electrocardiogram (ECG): understanding your heart’s electrical activity
A quick, non-invasive test to better understand your heart rhythm.
The electrocardiogram, commonly called an ECG, is a test that records the heart’s electrical activity.1 It can provide information on, among other things, the heart rate, the heart rhythm and the conduction of electrical signals.
At the Clinique IPS du Palais in Saint-Hyacinthe, the 12-lead ECG can be performed directly at the clinic as part of an assessment or follow-up, or at the request of a health professional.
The test
What is an ECG?
The electrocardiogram records the heart’s electrical signals using electrodes placed on the skin.
It does not produce electricity in the body: the device only records the heart’s natural electrical activity.7 The test is non-invasive and painless.1
The tracing is always interpreted in the clinical context: symptoms, history, medications, physical examination and, if needed, other investigations.
The ECG can be used, among other things, to assess:
- how fast the heart is beating;
- how regular the heart rhythm is;
- how the electrical impulse travels through the heart;
- certain electrical changes that may be associated with various heart conditions.
The heart’s electrical system
With every beat, an electrical impulse
The heart has its own electrical system.
The signal that triggers each heartbeat starts at the sinoatrial node and spreads from top to bottom, from the atria to the ventricles.2 The chambers of the heart thus contract in a coordinated way to pump blood. The ECG translates this activity into a tracing that the professional analyzes.
- Sinoatrial node
- Atria
- Ventricles
Indications
Why might an ECG be ordered?
Dizziness or feeling unwell
Depending on the context, certain rhythm abnormalities can contribute to dizziness, weakness, a light-headed feeling or sometimes a loss of consciousness. An ECG may then be part of the assessment.
Shortness of breath
Unusual shortness of breath can have cardiac as well as non-cardiac causes. Depending on the situation, an ECG may be ordered as part of the investigation.
Monitoring of certain medications
Some medications can affect the rhythm, the heart rate or certain intervals measured on the ECG. An ECG may therefore be ordered before or during treatment.
Assessment, procedure or follow-up
Preoperative assessment, medical check-up, follow-up of a known heart condition, or a baseline measurement of the heart’s electrical activity.
Chest pain or discomfort
The ECG is one of the tests used to assess certain types of chest pain, but pain that may be cardiac must not be assessed solely with an ECG in an outpatient clinic.
See below: when to call 911.
What the tracing shows
What can an ECG reveal?
An ECG can help detect, among other things, arrhythmias, a recent or ongoing heart attack, damage to the heart muscle or an enlarged heart.1
An abnormal ECG does not automatically mean that a serious disease is present. Conversely, a normal ECG does not rule out all heart disease.
In the appropriate context, it can help document:
- certain arrhythmias present at the time of the test, such as atrial fibrillation;3
- a heart rate that is too fast or too slow;
- electrical conduction disorders;
- signs consistent with current or past damage to the heart muscle;
- hypertrophy of certain chambers of the heart;
- or other electrical abnormalities.
Your appointment
How is an ECG done?
Positioning
You are positioned lying down.1
Electrodes
Adhesive electrodes are placed on the chest, arms and legs, then connected to the device.1
Recording
Stay still and relaxed: muscle movements can interfere with the tracing. The recording lasts only a few seconds.
End of the test
The electrodes are removed. Including setup, the test usually takes a few minutes.
Why is it called a “12-lead” ECG?
A standard ECG uses several electrodes to observe the heart’s electrical activity from different angles. These perspectives produce 12 electrical leads, like several viewpoints on the same phenomenon.
This provides a much more complete picture of the heart’s electrical activity than simply measuring the pulse.
Good to know
Do I need to prepare?
In most cases, no special preparation is needed and you do not need to fast.1
- wear clothing that is easy to remove from the chest area;
- if possible, avoid creams or oils on your chest on the day of the test;
- tell the professional about your medications and medical history.
A small area of hair may need to be cleared so the electrodes stick properly.
Is it painful?
No. The ECG is a non-invasive, painless test.1
You might only feel slight discomfort when the adhesive electrodes are removed.
Does the ECG send electricity into the body?
No. This is a common question.
The electrodes are only sensors: they record the electrical activity already produced by your heart and do not produce electricity.7
What is the difference between an ECG and a Holter?
Both record the heart’s electrical activity, but over very different periods of time.
The standard ECG is a very short recording: an electrical snapshot of the heart at the moment of the test.
The Holter or an extended cardiac monitor records the rhythm for several hours or several days.3 It is useful when symptoms are intermittent and do not occur during the ECG.7
Does a normal ECG mean my heart is normal?
No. This is an important distinction.
The ECG represents the heart’s electrical activity over a short period. Some abnormalities are intermittent: an arrhythmia may occur only occasionally.
In addition, during certain heart attacks (NSTEMI), the ECG does not show ST-segment elevation; blood tests, such as troponin, are also part of the diagnosis.4
Depending on the situation, the professional may recommend blood tests, extended cardiac monitoring, an echocardiogram, a stress test or an additional medical assessment.
Personal devices
ECG and smartwatches: are they the same thing?
Some watches and personal devices can record a simplified ECG.7
They can sometimes be useful for documenting certain rhythm irregularities, but they do not always replace a 12-lead medical ECG, which analyzes the heart’s electrical activity from several angles at once.
If your watch regularly indicates an abnormal rhythm or if you have symptoms, talk to a health professional.
When should you call 911 instead?
An ECG offered at a clinic by appointment does not replace emergency services. Heart & Stroke recommends calling 9-1-1 immediately if there are signs that may suggest a heart attack, including:5
- pain, pressure, tightness or discomfort in the chest;
- discomfort that may affect the arm, shoulder, back, neck or jaw;
- shortness of breath;
- sweating;
- nausea;
- dizziness.
The Government of Quebec also advises calling 911 for a person in cardiac arrest, unconscious or in respiratory distress.6
Do not delay an urgent assessment in order to get an ECG at a clinic first.
An ECG right here in Saint-Hyacinthe
At the Clinique IPS du Palais, we perform the 12-lead electrocardiogram on site. This simplifies your care pathway and makes it easier to send the information to the professional responsible for your follow-up.
Depending on your situation, the ECG can be performed:
- as part of a consultation;
- at the request of a health professional;
- as part of certain follow-ups;
- or as an additional test when indicated.
Electrocardiogram — 12-lead ECG$60
Frequently asked questions
Frequently asked questions about the ECG
How long does an ECG take?
The recording is very quick. Including placement of the electrodes, the test usually takes only a few minutes.
Do you need to fast?
Usually not.
Can I take my medications before the test?
As a general rule, yes, unless otherwise instructed by the professional who ordered the test.
Can you have an ECG if you have a pacemaker?
Yes. The ECG can show, among other things, the heart’s electrical activity and certain elements related to how a pacemaker is working.
Is it dangerous during pregnancy?
The ECG is an external test that records the heart’s electrical activity and does not emit ionizing radiation.
Can an ECG detect all arrhythmias?
No. If the arrhythmia is intermittent and absent during the few seconds of the recording, the ECG may be normal. Prolonged monitoring may sometimes be necessary.
Key takeaways
The electrocardiogram is a simple, quick and non-invasive test that records the heart’s electrical activity. It provides information on your heart rate, your rhythm, the heart’s electrical conduction and certain cardiac abnormalities.
However, it must be interpreted in light of your clinical condition and does not replace a medical assessment or additional tests when these are needed.
Sources
- Heart and Stroke Foundation of Canada (Heart & Stroke). Électrocardiogramme (ECG). Undated, accessed October 5, 2026. coeuretavc.ca
- Heart & Stroke. Comment fonctionne le cœur. Undated, accessed October 5, 2026. coeuretavc.ca
- Public Health Agency of Canada. Fibrillation auriculaire. Modified September 18, 2026, accessed October 5, 2026. canada.ca
- Heart & Stroke. Crise cardiaque. Undated, accessed October 5, 2026. coeuretavc.ca
- Heart & Stroke. Signes d’urgence : quand appeler le 9-1-1. Undated, accessed October 5, 2026. coeuretavc.ca
- Government of Quebec. Quand et comment utiliser le 911 au Québec. Updated April 10, 2026, accessed October 5, 2026. quebec.ca
- Mayo Clinic Staff. Electrocardiogram (ECG or EKG). Mayo Clinic, updated September 11, 2026, accessed October 5, 2026. mayoclinic.org
The information on this page is provided for informational purposes and does not replace an assessment by a health professional.