Within an in vivo intact heart, the action/response of the sympathetic nervous system is driven by precisely timed releases of a catecholamine, which is a process that determines the concentration of calcium ions in the cytosol of cardiac muscle cells.
This is done by a number of mechanisms:[citation needed] Decreasing contractility is done primarily by decreasing the influx of calcium or maintaining lower calcium levels in the cytosol of cardiac myocytes during an action potential.
This is done by a number of mechanisms:[citation needed] A measurable relative increase in contractility is a property of the myocardium similar to the term "inotropy".
The ancient herbal remedy digitalis appears to have both inotropic and chronotropic properties that have been recorded encyclopedically for centuries and it remains advantageous today.
[citation needed] Under one existing model [citation needed], the five factors of myocardial performance are considered to be By this model, if myocardial performance changes while preload, afterload, heart rate, and conduction velocity are all held constant, then the change in performance must be due to a change in contractility.