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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) 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 or S wave amplitude (the larger of the two) 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).

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