Is an ECG painful or dangerous?

No, an ECG is a completely non-invasive and painless procedure. It involves placing small electrodes (sticky patches) on the skin, which simply detect the electrical signals naturally produced by your heart. There is no electrical current sent into your body, and thus no risk of electric shock or any other harm. It's a very safe and routine test performed frequently in medical settings.

How long does an ECG take to perform?

A standard resting ECG is a very quick test, typically taking only about 5 to 10 minutes from start to finish. The actual recording of the heart's electrical activity usually lasts for less than a minute. The preparation, which includes placing the electrodes, takes the majority of the time. Other types of ECGs, like stress ECGs or Holter monitoring, can take longer or involve continuous recording over 24-48 hours.

Can an ECG detect all heart problems?

While an ECG is an incredibly powerful diagnostic tool, it cannot detect *all* heart problems. It's excellent for identifying electrical abnormalities like arrhythmias, conduction blocks, and signs of heart attack or ischemia. However, it may not always reveal structural issues (like valve problems or congenital defects) or intermittent arrhythmias that don't occur during the brief recording period. Other tests, such as echocardiograms or stress tests, might be needed for a comprehensive evaluation.

What is the difference between an ECG and an echocardiogram?

An ECG records the *electrical activity* of the heart, showing how electrical impulses travel and trigger contractions. It provides information about heart rate, rhythm, and electrical conduction. An echocardiogram, on the other hand, uses *sound waves* (ultrasound) to create moving images of the heart. It provides detailed information about the heart's structure, chamber size, valve function, and blood flow. Both are crucial but provide different types of information.

Why is the P wave smaller than the QRS complex?

The P wave represents the electrical depolarization of the atria, while the QRS complex represents the electrical depolarization of the ventricles. The ventricular muscle mass is significantly larger and thicker than the atrial muscle mass, as the ventricles are responsible for pumping blood to the entire body (left ventricle) and lungs (right ventricle). A larger muscle mass undergoing depolarization generates a stronger electrical signal, which results in a larger amplitude QRS complex compared to the P wave.

Electrocardiogram

Biology

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Version 1Updated 22 Mar 2026

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The electrocardiogram (ECG or EKG) is a graphical recording of the electrical activity of the heart, specifically the changes in electrical potential that occur during the cardiac cycle. It represents the summation of action potentials generated by the depolarization and repolarization of cardiac muscle cells, detected by electrodes placed on the body surface. This non-invasive diagnostic tool pro…

Quick Summary

The Electrocardiogram (ECG or EKG) is a non-invasive diagnostic test that records the electrical activity of the heart over time. It works by detecting the tiny electrical impulses generated by the heart's specialized conduction system (SA node, AV node, Bundle of His, Purkinje fibers) as they spread through the cardiac muscle, causing depolarization and repolarization.

The resulting graphical tracing displays characteristic waves and segments: the P wave signifies atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave indicates ventricular repolarization.

The PR interval measures conduction time from atria to ventricles, and the ST segment reflects the plateau phase of ventricular action potentials. By analyzing the rate, rhythm, and morphology of these waveforms, clinicians can diagnose a wide range of cardiac conditions, including arrhythmias, myocardial ischemia, and hypertrophy, making it a fundamental tool in cardiovascular assessment.

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Key Concepts

P Wave and Atrial Activity

The P wave is the initial positive deflection on the ECG, signifying the electrical impulse originating from…

QRS Complex and Ventricular Activity

The QRS complex is the most prominent part of the ECG, representing the rapid depolarization of the…

ST Segment and Myocardial Ischemia

The ST segment is the flat, isoelectric (baseline) line between the end of the S wave and the beginning of…

P Wave: — Atrial depolarization.

QRS Complex: — Ventricular depolarization.

T Wave: — Ventricular repolarization.

PR Interval: — Start of P to start of QRS. Normal:

0.12 - 0.20,\text{s}

. Reflects AV nodal delay.

ST Segment: — End of S to start of T. Isoelectric. Elevation/depression indicates ischemia/injury.

QT Interval: — Start of Q to end of T. Total ventricular electrical activity.

Heart Rate: — Normal

60-100,\text{bpm}

. Tachycardia

>100,\text{bpm}

. Bradycardia

<60,\text{bpm}

Atrial repolarization is masked by the QRS complex.

Pump Quietly, Really Slowly, Then Recover.

Pump: P wave = Atrial Pumping (depolarization).

Quietly, Really Slowly: QRS complex = Ventricular Quick Rush Systole (depolarization).

Then Recover: T wave = Ventricular Recovery (repolarization).

(The 'Quietly, Really Slowly' part is a bit of a stretch for QRS, but the 'P' for pumping and 'T' for recovery are strong associations.)