## Core Concept
The electrical axis of the heart, also known as the cardiac axis, is the direction in which the electrical impulse travels through the heart during depolarization. It is typically measured in the frontal plane and expressed in degrees. A normal cardiac axis is crucial for efficient contraction of the heart.

## Why the Correct Answer is Right
The correct answer, , indicates that the normal axis of the heart is between -30 degrees and +90 degrees. This range allows for optimal ventricular depolarization. The axis is determined by the net direction of ventricular depolarization as seen in the limb leads of an electrocardiogram (ECG). A normal axis suggests that the electrical conduction system of the heart is functioning properly.

## Why Each Wrong Option is Incorrect
* **Option A:** This option suggests an axis that is too leftward, which could indicate left ventricular hypertrophy or a conduction abnormality.
* **Option B:** This option represents a right axis deviation, which can be seen in conditions such as right ventricular hypertrophy or certain types of heart block.
* **Option D:** This option indicates a marked left axis deviation, which is often associated with conditions like left anterior fascicular block.

## Clinical Pearl / High-Yield Fact
A useful mnemonic to remember the normal range of the cardiac axis is that it should be "between -30 and +90 degrees". Outside this range, it may indicate pathology. For example, a left axis deviation ( +90 degrees) can be seen in right ventricular hypertrophy.

## Correct Answer: .