u/cardiolab_

First, a quick update: CardioLab is now ECG Sweep! The new name keeps it clear of an existing electrophysiology product.

Phase I is done. ECG Sweep now covers the core rhythms and arrhythmias every clinician and student needs to know, each one animated so you can watch it happen rather than memorize a strip.

Since I started sharing this, i have been getting requests to use it in teaching materials and curricula. It is ready for that now, and it's free to use with attribution. If you teach ECGs, I would love for you to try it with your students. That is what this project has always been about: making ECGs click by letting you see them.

New in this update: ECG flashcards, for quick review and games. Learning ECGs can actually be fun!

Next up is Phase II, and it is the reason the 12-lead foundation had to come first. This phase is all about clinical practice:

- What if you could watch a drug take effect without waiting for a real patient? You know, like visualize adenosine stop an SVT?

- What if you could run your ACLS algorithms as a realistic case, not just a flowchart?

- Can STEMIs be made intuitive, so you see the territory and the culprit artery instead of just reciting leads?

It will be the most ambitious part of the project yet, but the groundwork is in place.

Your feedback has shaped this from the start. It has caught mistakes and made the simulation more accurate, and having extra expert eyes on it is how I make sure I'm not teaching errors. So please keep it coming: corrections, ideas and anything you would like to see in Phase II.

Have fun exploring, and thank you!

First, a quick update: CardioLab is now ECG Sweep! The new name keeps it clear of an existing electrophysiology product.

Phase I is done. ECG Sweep now covers the core rhythms and arrhythmias every clinician and student needs to know, each one animated so you can watch it happen rather than memorize a strip.

Since I started sharing this, i have been getting requests to use it in teaching materials and curricula. It is ready for that now, and it's free to use with attribution. If you teach ECGs, I would love for you to try it with your students. That is what this project has always been about: making ECGs click by letting you see them.

New in this update: ECG flashcards, for quick review and games. Learning ECGs can actually be fun!

Next up is Phase II, and it is the reason the 12-lead foundation had to come first. This phase is all about clinical practice:

- What if you could watch a drug take effect without waiting for a real patient? You know, like visualize adenosine stop an SVT?

- What if you could run your ACLS algorithms as a realistic case, not just a flowchart?

- Can STEMIs be made intuitive, so you see the territory and the culprit artery instead of just reciting leads?

It will be the most ambitious part of the project yet, but the groundwork is in place.

Your feedback has shaped this from the start. It has caught mistakes and made the simulation more accurate, and having extra expert eyes on it is how I make sure I'm not teaching errors. So please keep it coming: corrections, ideas and anything you would like to see in Phase II.

Have fun exploring, and thank you!

I am genuinely excited to share this with you all. A 12-lead simulation has been one of the most requested feature, and it is finally live. Thank you so much for your patience!

My main goal was to make reading a 12-lead as intuitive as possible. I didn't just want to show what an abnormal ECG looks like, but why it looks that way. Here are a few features designed to help with that:

• Follow the beat: Watch how the electrical signal starts and spreads. The QRS complex is colour-coded by the part of the heart generating it (septum, left ventricle, late right ventricle), so you can actually see why a bundle branch block creates the shapes it does.
• Compare with normal: Toggle on "Normal" to overlay a standard grey ECG behind the active tracing. This makes the differences stand out clearly, lead by lead.
• Inspect any lead: Pause the tracing and click/tap any lead to open it up. You can step through the P, PR, QRS, ST, T and QT intervals, see exactly how they are measured, and compare them side-by-side with a normal ECG.

It is honestly way easier to see in action than to describe, so I highly recommend taking it for a spin.

What’s new in the 12-lead module:

• Conduction: Right bundle branch block & Left bundle branch block (complete and incomplete).
• Electrolytes:
  • Hyperkalaemia: Shown as a progression (peaked T waves at K⁺ 6.0 → prolonged PR & wide QRS → sine wave → VF).
  • Hypokalaemia: Shown as a progression (flat T & U waves → ST depression → Torsades de Pointes).

A quick request:
A 12-lead has way more moving parts than the single-lead rhythms, and since I have built this entirely on my own, it is easy for small mistakes to slip through. The model strictly follows standard textbooks and published criteria, but if you spot anything off; whether it is a wave, a number, or a typo in an article, please let me know! I will fix it as quickly as possible.

All feedback is incredibly welcome.

Hope you all have a great weekend, and I would love to hear what you think!

Let’s talk about the cardiac axis. It is arguably one of the most confusing concepts in ECG interpretation.

I struggled with it myself for the longest time. What does the "direction" of a vector actually mean in practice? And when someone says, "just look at lead I and aVF," what are you actually looking at?

Over the past week, I have been building an interactive tool to help demystify this. It is a live simulation: you can drag the axis around a dial, and all six limb leads redraw in real-time as you move it.

It walks you step-by-step through the three most common methods for determining the axis, based on whatever angle you set:

1. The Quadrant Method: Checking if the QRS is positive or negative in leads I and aVF.
2. The Isoelectric Method: Finding the equiphasic lead and knowing the axis is perpendicular to it. (default).
3. The Three-Lead Method: Using the quadrant method plus lead II to determine if a leftward axis is still normal, or if it has crossed the −30° threshold into true Left Axis Deviation.

I built this with students in mind, hoping it finally makes the concept "click." It should also be a handy tool for educators who want to demo axis determination live and point out those classic ECG gotchas.

Give it a try here

I would really appreciate any feedback, bug reports, or corrections! It is optimized for desktop, but it works on mobile too. Let me know what you think!

Hey everyone,

A few weeks ago, i posted about building a live, moving ECG simulator because static textbook images weren't cutting it for learning.

First, a massive thank you. The response from the community was incredible. I read every single comment and the feedback was exactly what I needed to make this tool genuinely useful for students, nurses, paramedics, residents, practitioners and everyone.

I have spent the last few weeks heads down coding, and I am excited to share that I have implemented some top suggestions.

Here is what is new in CardioLab based entirely on your feedback:

1. A Dedicated, Deep-Dive SVT Section
Many of you pointed out that distinguishing between different narrow-complex tachycardias is a major pain point. I have now isolated SVT into its own dedicated section so you can compare and contrast the mechanisms side-by-side.

2. New High-Yield Rhythms Added:

• AVNRT (Atrioventricular Nodal Reentrant Tachycardia)
• AVRT (Atrioventricular Reentrant Tachycardia)
• Focal Atrial Tachycardia
• WPW (Wolff-Parkinson-White syndrome, with live delta wave visualization)

3. Overhauled "Clinical Notes" for Learners
You mentioned the notes needed to be more actionable for studying. I have completely rewritten the information panel for SVT rhythms to be highly structured for learners. (I am in the process of updating all rhythms).

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I am a builder, and this project is entirely driven by what you actually need in the trenches and on the wards.

• What rhythms are you still struggling to find good, live examples of? Reply with your requests, and I will prioritize them in the next build.
• Keep the corrections coming. If you spot a morphological inaccuracy, an interval that looks off, or a clinical note that needs tweaking, tell me. I want this to be the most medically accurate free resource on the web.

You can test all the new rhythms and the updated notes here: cardiolab.io/simulator

TL;DR: You gave me great feedback on my free live ECG simulator. I listened. I just added a dedicated SVT section, new rhythms (AVNRT, AVRT, Focal AT, WPW) and completely overhauled the clinical notes to be more learner-friendly. Tell me what to build next!

TL;DR: I built a free live ECG simulator because I wanted more practice with moving rhythms, not just static ECGs. Looking for feedback from EM clinicians and learners.

Backstory: I am a medical doctor and software developer.

You know how we spend hours looking at static strips and textbook examples, but then you see a rhythm continuously on a monitor and it somehow feels different. This is my story with learning ecgs, static rhythms on an ECG paper just weren't intuitive.

So I built CardioLab — a free, browser-based ECG simulator with live scrolling rhythms and 12-lead ECGs. The idea is pretty simple: more reps, but with rhythms that actually move. (well not so simple)

You can watch AF, atrial flutter, AV blocks, VT, torsades, SVT and more rhythms unfold rather than just looking at a screenshot.

I'm still building it, and I would really like feedback from everyone. What would actually make this useful for you?

• Which rhythms do you want more examples of?
• Would different presentations of the same rhythm be useful?
• What ECGs do you wish you could practise more?
• What would make this useful during teaching or exam prep?

I have already gotten feedback for SVT with aberrancy, Brugada patterns, different conduction ratios and more, so I am adding things as I go.

If you have a few minutes, try it and tell me what I've got wrong or what you'd add.

ps: I am a doctor who codes, not a specialist, so I genuinely rather hear that something is wrong and fix it. I would appreciate all feedback and critique to improve the simulation, accuracy is important for learning.

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