Final answer:
Heart failure is a chronic condition that impairs the ability of the heart to adequately pump blood and supply oxygen to the body's cells. It is caused by dysfunction in cardiac muscle cells and a decrease in the availability of calcium ions for muscle contractions. This leads to a decrease in cardiac function and output.
Step-by-step explanation:
Heart failure is a chronic condition in which cardiac muscle cells cannot contract forcefully enough to keep body cells adequately supplied with oxygen. It occurs when the endoplasmic reticula of cardiac muscle cells do not function properly, leading to an insufficient number of calcium ions available for contractions. This results in a decrease in cardiac function and output as the heart is unable to pump blood with sufficient force to transport oxygenated blood to all the vital organs.