CVS Practice Test 2025 – Complete Exam Preparation

The innervation of the heart is predominantly influenced by the sympathetic nervous system, which prepares the body for 'fight or flight' responses. Sympathetic fibers, primarily arising from the spinal cord segments T1 to T4, increase the heart rate, enhance the force of contraction, and improve blood flow to the heart and muscles when needed. This system also plays a crucial role in redistributing blood flow during physical activity or stress.

While the parasympathetic system, primarily mediated by the vagus nerve, does exert some control over the heart—mainly by decreasing heart rate and promoting a state of rest and recovery—it is the sympathetic system that has a stronger and more immediate impact on heart function during situations requiring increased cardiac output. This is why the characterization of heart innervation leans towards sympathetic predominance.

The other options suggest an incorrect balance or scope of innervation, either implying equal influence or limited sympathetic action to the ventricles only, which misrepresents the broader role of sympathetic fibers throughout the heart.