Parasympathetic (vagal) nerves leave the vagal nuclei within the medulla as preganglionic efferent vagal fibers. These preganglionic efferent fibers are relatively long and do not synapse until they reach their target organ (e.g., the heart).
medical Definition of isovolumetric : of, relating to, or characterized by unchanging volume; especially: relating to or being an early phase of ventricular systole in which the cardiac muscle exerts increasing pressure on the contents of the ventricle without significant change in the muscle fiber length and the ventricular volume remains constant
When the volume of a thermodynamic system is constant, it does zero work on the surroundings. Then W = 0, and In an isochoric process, all the energy added as heat remains in the system as an increase in internal energy. Heating a gas in a closed constant-volume container is an example of an isochoric process.