There is a reasonable objection to learning rhythms by their look: it encourages guessing. The objection is fair, and the answer is that recognition and analysis do different jobs. Recognition generates a hypothesis in half a second. Analysis confirms or kills it. What gets people into trouble is skipping the second half, not having the first.
These are the eight worth having instantly available, each with the one feature that identifies it.
1. Normal sinus rhythm
The tell: a P wave before every QRS, a QRS after every P wave, rate 60–100, regular.
Worth listing first because you cannot call something abnormal until you know precisely what normal looks like. If you cannot say why a strip is sinus, you are not recognising sinus — you are recognising "nothing jumped out".
2. Sinus bradycardia
The tell: everything about sinus rhythm, but under 60.
The interpretive work is not on the strip, it is at the bedside. An athlete at 48 and a patient on beta-blockers at 48 with syncope produce a similar trace and entirely different decisions.
3. Sinus tachycardia
The tell: sinus, over 100, and — importantly — it has a reason.
Sinus tachycardia is a response, not a disease. Rate-controlling it without asking what is driving it treats the number rather than the pain, the hypovolaemia, the sepsis or the pulmonary embolus.
4. Atrial fibrillation
The tell: irregularly irregular, with no discernible P waves.
Both halves matter. Irregularity alone does not make AF, and a chaotic baseline that still marches out regularly is more likely to be artefact.
5. Atrial flutter
The tell: sawtooth flutter waves, usually best seen in the inferior leads, often at an atrial rate near 300.
With 2:1 conduction the ventricular rate lands near 150 and the flutter waves hide inside the QRS and T waves. A rock-steady 150 should make you look specifically for the second flutter wave you have not spotted yet.
6. Supraventricular tachycardia
The tell: narrow-complex, regular, fast — typically 150–250 — with P waves absent or buried.
7. Ventricular tachycardia
The tell: broad-complex, regular, fast.
Treat a broad-complex tachycardia as ventricular tachycardia until proven otherwise. This is the single most useful default in rhythm interpretation. Getting VT wrong and calling it SVT with aberrancy is considerably more dangerous than the reverse — particularly in anyone with known ischaemic heart disease, where the prior probability of VT is high.
8. Third-degree (complete) AV block
The tell: P waves and QRS complexes that are each regular, at different rates, with no relationship between them.
March out the P waves alone, then the QRS complexes alone. Two independent regular rhythms is the finding. This is where the habit of asking "P before every QRS?" and "QRS after every P?" as two separate questions pays for itself.
Test the recognition
See whether you can name these against a clock
Einthoven puts these rhythms in front of you as timed traces at clinical scale, then explains the answer whether you got it right or wrong. Three traces, no account needed.
Try three traces free →The three pairs that actually get confused
Nobody mixes up normal sinus rhythm with ventricular tachycardia. The errors cluster in three specific pairs.
Atrial flutter with 2:1 block vs sinus tachycardia
Both regular, both near 150. Look for flutter waves in II, III and aVF. A rate that sits at exactly 150 and refuses to drift is far more suggestive of flutter — sinus tachycardia normally varies a little from beat to beat.
Ventricular tachycardia vs SVT with aberrancy
Both broad, both fast, both regular. Features favouring VT include AV dissociation, capture or fusion beats, very broad QRS, and extreme axis. In practice: assume VT, and let the features that argue against it be found rather than assumed.
Atrial fibrillation vs multifocal atrial tachycardia
Both irregular. The difference is the P waves — AF has none, MAT has at least three distinct P wave morphologies. If you can see P waves at all, it is not AF.
Offline drilling
EKG Rhythm Flashcards — 27 printable cards
The eight rhythms above plus nineteen more, one per card, for spaced repetition away from a screen. Built for nursing and medical students. €20.91 · instant digital download.
View on Etsy →How to actually learn these
Reading a list once does very little. The evidence on rhythm-strip interpretation suggests students need roughly 34 practice cases and under two hours of deliberate practice to reach 75% accuracy — repetition against feedback, not re-reading.
Practically: work in short sessions, always commit to an answer before revealing it, and pay more attention to the ones you got wrong than the ones you got right. Cards are good for the recall half. Timed traces are good for the recognition half. You need both, because in the resuscitation room nobody hands you the rhythm name and asks for the features.
References
- Van Gelder IC, Rienstra M, Bunting KV, et al. 2024 ESC Guidelines for the management of atrial fibrillation, developed in collaboration with EACTS. Eur Heart J. 2024;45(36):3314–3414. PMID:39210723
- Zeppenfeld K, Tfelt-Hansen J, de Riva M, et al. 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J. 2022;43(40):3997–4126. PMID:36017572
- Surawicz B, Childers R, Deal BJ, et al. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part III — Intraventricular Conduction Disturbances. J Am Coll Cardiol. 2009;53(11):976–981.
- Hartman ND, Wheaton NB, Williamson K, et al. Quantifying the medical student learning curve for ECG rhythm strip interpretation using deliberate practice. PMC6737266.