An electrocardiogram (ECG or EKG) is a recording of the electrical activity generated by the heart with each beat. Electrodes placed on the skin detect tiny voltage differences produced as the cardiac impulse spreads through heart muscle, and these are plotted over time as a characteristic waveform.

A typical ECG tracing displays three main deflections per cardiac cycle: the P wave (atrial depolarisation), the QRS complex (ventricular depolarisation — the electrical event that triggers contraction), and the T wave (ventricular repolarisation). The intervals between these deflections — PR interval, QRS duration, QT interval — carry important diagnostic information.

The standard clinical ECG records 12 leads simultaneously, each offering a different geometric 'view' of the heart. This simulator renders a single-channel rhythm strip analogous to Lead II, which is most commonly used for rhythm analysis.

Normal sinus rhythm establishes the baseline — a regular rhythm driven by the sinoatrial (SA) node at a rate of 60–100 bpm. The P wave precedes every QRS complex with a consistent PR interval, and the QRS is narrow.

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. The simulator models its hallmark features: absent discrete P waves, irregular baseline fibrillatory activity, and an irregularly irregular ventricular response. AF significantly increases stroke risk due to stasis in the left atrial appendage.

Atrial flutter shows a characteristic sawtooth flutter baseline at approximately 300 bpm with regular ventricular conduction at a fixed ratio (commonly 2:1 or 4:1). The flutter waves are best seen between QRS complexes.

Supraventricular tachycardia (SVT) presents as a regular narrow-complex tachycardia at 140–200+ bpm. P waves may be buried within or occur just after the QRS complex depending on the mechanism involved.

Ventricular tachycardia (VT) is a wide-complex, rapid tachycardia originating in the ventricular myocardium. It is a potentially life-threatening rhythm requiring prompt assessment. The simulator renders broad QRS complexes at a rate above 120 bpm.

Premature ventricular contractions (PVCs) appear as isolated wide, bizarre QRS complexes interrupting an otherwise normal baseline rhythm. Occasional PVCs are common and often benign; frequent PVCs may warrant investigation.

Bradycardia refers to any rhythm below 60 bpm. The simulator shows a slow but otherwise normal-morphology sinus rhythm, reflecting sinus bradycardia.

Complete heart block (third-degree AV block) demonstrates complete dissociation between atrial and ventricular activity — P waves march at their own rate with no relationship to the QRS complexes, which are driven by a slow, independent ventricular escape rhythm.

Select a rhythm preset from the menu to load the corresponding waveform pattern. You can adjust the heart rate and amplitude using the controls provided — this demonstrates how the same rhythm type appears at different rates and signal strengths.

Use the simulator to compare rhythms side by side in your memory: start with Normal sinus rhythm, then switch to AF to immediately appreciate the irregular baseline and absent P waves. Pattern recognition through repetition is central to ECG interpretation skill.

The simulator is designed as a study companion — useful for medical and nursing students, paramedics, and anyone building foundational cardiac rhythm recognition skills before working with clinical recordings.

The PR interval (normal: 120–200 ms) represents the time from atrial depolarisation to the onset of ventricular depolarisation. A prolonged PR interval indicates first-degree AV block; a progressively lengthening PR suggests second-degree (Wenckebach) block.

The QRS duration (normal: 60–100 ms in adults) reflects ventricular depolarisation speed. A broad QRS (>120 ms) suggests bundle branch block, ventricular pacing, or an origin of the impulse within the ventricular myocardium (e.g., VT or PVC).

The QT interval (normal: 360–440 ms, varies with heart rate) represents combined depolarisation and repolarisation of the ventricles. Corrected QT (QTc) above 450 ms in males or 460 ms in females indicates long QT, which carries risk of torsades de pointes — a potentially fatal arrhythmia.