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
anisotropic. 1. having unlike properties in different directions. 2. doubly refracting, or having a double polarizing power. 3. in cardiac physiology, having nonuniform conduction; used to describe the nonuniform characteristics of the myocardium in the direction perpendicular to the conduction direction of a fiber. See also isotropic.