ECG (electrocardiography) is a fast, painless and cheap recording of the heart's electrical activity through electrodes on the skin. It is the basic method of cardiology: a heart examination often starts with it.
An ECG shows how the heart contracts and conducts impulses: the rate and rhythm, signs of strain, ischemia and a past heart attack. Its individual elements — the QRS complex and the QT interval — carry diagnostic information.
What an ECG shows
An ECG helps detect: rhythm disturbances (arrhythmias, atrial fibrillation), signs of ischemia and myocardial infarction, conduction blocks, strain and hypertrophy of the heart chambers, as well as electrolyte shifts and the effect of medications.
For chest pain an ECG is the first and key test, often together with troponin.
How it is done and its limitations
An ordinary ECG takes a couple of minutes: electrodes are placed on the chest, arms and legs, and you lie still. Almost no preparation is needed.
The main limitation is that an ECG reflects only a brief moment. If an arrhythmia or ischemia occurs episodically, an ordinary recording may “miss” it. In that case 24-hour monitoring (Holter) or a stress ECG is used. An ECG does not show the structure and pumping function of the heart — for that you need echocardiography.
Assess your heart's age
An ECG assesses the heart's electrical activity; assess your long-term cardiac risk:
Frequently asked questions
What does an ECG show?
The heart's electrical activity: the rate and rhythm, conduction disturbances, signs of ischemia and a past heart attack, chamber strain. It is a fast basic test, but it reflects only the moment of recording and does not show the heart's structure.
How does an ECG differ from an echocardiogram?
An ECG records the heart's electrical activity (rhythm, ischemia), while echocardiography (a heart ultrasound) shows its structure and pumping function — chamber sizes, valves, ejection fraction. These are different, complementary methods.
Why can heart problems occur with a normal ECG?
An ordinary ECG lasts only a few minutes and may miss episodic arrhythmias or ischemia. In such cases 24-hour monitoring (Holter) or a stress ECG is ordered, and for assessing the heart's structure — an echocardiogram.
Related terms
Sources
- MedlinePlus (NIH) — Electrocardiogram (ECG or EKG)
- American Heart Association — Electrocardiogram (ECG or EKG)
- Electrocardiogram — StatPearls (NCBI)