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Heart Axis Calculator

We have improved our heart axis calculator to make it even more accurate. Now you can calculate the QRS axis as described in the classic formula, with leads I and III (until now we used aVF).

Therefore, if you want to get the exact value of the heart axis, you only have to enter the QRS net amplitude (R wave - S wave - Q wave) in leads I and III, and clicking the "calculate" button.

Remember must use a minus sign if the QRS is predominantly negative.

Heart axis

Heart Axis Cálculator

QRS amplitude
in lead I


QRS amplitude
in lead III


Click on "Calculate" button

  • Normal heart axis: Between -30º and 90º.
  • Right-axis deviation: Between 90º and 180º.
  • Left-axis deviation: Between -30º and -90º.
  • Extreme axis deviation: Between 90º and 180º.

Remember, this calculator is not 100% reliable, and it is not a substitute for traditional methods of heart axis calculation, nor electrocardiogram evaluation made by a doctor or competent professional.

Net QRS Amplitude for Calculation of the Heart Axis

To use the heart axis calculator, you have to calculate the net amplitude of the QRS (see QRS morphologies).

Subtract the Q wave and the S wave amplitude from the R wave amplitude. If the result is negative, the minus sign must be used (for example, -2).

Heart Axis Calculator, positive lead

QRS = 12 mm.

Heart Axis Calculator, slightly positive lead

QRS = 1 mm (R wave: 7 mm - S Wave: 6 mm).

Heart Axis Calculator, negative lead

QRS = -6 mm (R Wave: 2 mm - S Wave: 8 mm).

We have improved the Heart Axis Calculator

If you have previously used our heart axis calculator you will notice that we have replaced lead aVF with lead III. Why?

There are two reasons for this.

The first reason is because it is as close as possible to the manual method of exact calculation of the QRS axis, which is based on transferring the amplitude of leads I and III to the hexaxial reference system and measuring the angle (see how to calculate the heart axis).

The second reason is that using a bipolar and a unipolar lead (I and aVF) tends to make errors in the calculation, because the method of obtaining the EKG information is different and therefore the amplitudes of the QRS complexes are not fully comparable.

With the new formula, two bipolar leads are used, which are therefore equivalent.

Why have we not used this method of calculating the heart axis before?

Because determining the mathematical formula that allows the calculation has been much more complex, to the point that we have not observed this way of calculating the axis on another website, Most of these websites use, as we did, the leads I and aVF.

So we are pleased to assure you that with this improvement of our axis calculator, you will be able to get a value closer to the real heart axis.

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