Einthoven's Triangle

Drag the cardiac vector and the three limb leads redraw in real time. The relationship between them stops being an equation to memorise and becomes something you watch happen.

Using it in a teaching session

Set the vector to a normal axis, then ask the room to predict what lead I will look like before you rotate it leftward. Predicting and then seeing the answer sticks far better than being told.

Lead reversal is worth five minutes on its own — swap the arm leads and let people work out from the tracings alone which cable is where.

What the model simplifies

The triangle is treated as equilateral and the torso as a uniform conductor. This is the standard teaching assumption rather than physiological reality, and it is worth naming that out loud when you use it.