During exercise, sympathetic input to the heart is increased. Stroke volume is often maintained, or even increased, even though heart rate is also increasing. How is this possible

1. Sympathetic input increases ventricular contractility, thereby increasing stroke volume.

2. Sympathetic input decreases conduction time within the heart, decreasing the delay between atrial and ventricular contractions.

3. Sympathetic input increases the speed of ventricular contraction.

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