An electrocardiogram (ECG) records the heart’s electrical activity to detect abnormal rhythms (arrhythmias), signs of reduced blood flow or heart attack, conduction blocks, and chamber enlargement. It helps assess effects of medications or electrolyte disturbances, monitor pacemaker function, and guide diagnosis of chest pain or syncope. The test is quick, noninvasive, and commonly used as an initial cardiac evaluation.

A normal ECG shows sinus rhythm at 60–100 bpm, normal electrical axis, P waves before each QRS, PR interval 120–200 ms, QRS duration <120 ms, and an appropriately corrected QT interval. There should be no pathological Q waves, significant ST‑segment elevation or depression, or abnormal T‑wave inversion. Overall waveforms, intervals and morphology fall within expected ranges for the patient's age and clinical context.

A standard 12‑lead ECG typically takes about 5–10 minutes from start to finish. Most time is spent attaching electrodes and ensuring correct placement; the actual tracing is recorded in a few seconds. In routine clinic settings allow 10–15 minutes for setup, explanation and any repeats. In emergencies ECGs are performed immediately; ambulatory monitoring (Holter) is a separate, longer test.

The five key ECG points are: P wave — atrial depolarization; PR interval — conduction time from atria through the AV node; QRS complex — ventricular depolarization and duration; ST segment — the isoelectric period between depolarization and repolarization where ischemic changes appear; and T wave — ventricular repolarization. Assessing these evaluates rate, rhythm, conduction, and ischemia.

A normal ECG is reassuring but not definitive. It can miss intermittent arrhythmias, early coronary artery disease, structural problems, or silent ischemia. If you have chest pain, breathlessness, fainting, palpitations, or significant risk factors, further tests (blood tests, echocardiogram, stress testing, Holter monitor) may be needed. Discuss results and next steps with your clinician.

Wear loose, comfortable clothing so you can expose your chest, wrists and ankles for electrode placement — a front‑opening shirt or easily removable top is ideal. Remove bras, jewelry and metal accessories that interfere with leads. Avoid heavy lotions, oils or powder on your skin. Expect staff to provide a gown and to trim small chest‑hair patches if needed for good electrode contact.