Final answer:
Sympathetic stimulation increases the contractile strength of the heart muscle, resulting in a greater stroke volume and a more efficient heartbeat, preparing the body to deal with increased physical demands.
Step-by-step explanation:
The increase in contractile force caused by sympathetic stimulation allows the ventricle to pump more blood with each beat, effectively increasing the stroke volume (SV) and decreasing the end-systolic volume (ESV). This is because sympathetic stimulation acts as a positive inotropic factor, which increases the metabolic rate and the force of contraction of the heart muscle. With sympathetic stimulation, neurotransmitters like norepinephrine (NE) and hormones such as epinephrine enhance the contractility of the cardiac muscles by binding to cardiac muscle cell receptors and increasing the influx of calcium ions, which are essential for muscle contraction. This results in more powerful and efficient heartbeats, enabling the heart to cope with increased physical demands or stress.