The normal QRS axis typically lies in which quadrant and range?

• A. Lower right quadrant, 0 to 90 degrees
• B. Upper left quadrant, -180 to -90 degrees
• C. Lower left quadrant, -90 to 0 degrees
• D. Upper right quadrant, 90 to 180 degrees

Answer: (A)

The QRS axis is the net direction of ventricular depolarization in the frontal plane, so its normal orientation points toward the lower-right portion of the frontal-plane diagram. In a healthy heart, this axis falls in the range of 0 to 90 degrees, which places it in that lower-right quadrant. This is why a normal QRS axis is described as being within 0 to 90 degrees on the frontal plane, aligning with a typical pattern of positive QRS complexes in leads that reflect this direction. The other quadrants correspond to angles that would indicate deviations from normal axis—upper left, lower left, or upper right—so they aren’t consistent with the normal axis.