The pathophysiology is not well understood, but a sudden massive surge of catecholamines such as adrenaline and norepinephrine from extreme stress or a tumor secreting these chemicals is thought to play a central role. Excess catecholamines, when released directly by nerves that stimulate cardiac muscle cells, have a toxic effect and can lead to decreased cardiac muscular function or "stunning". Further, this adrenaline surge triggers the arteries to tighten, thereby raising blood pressure and placing more stress on the heart, and may lead to spasm of the coronary arteries that supply blood to the heart muscle. This impairs the arteries from delivering adequate blood flow and oxygen to the heart muscle. Together, these events can lead to congestive heart failure and decrease the heart's output of blood with each squeeze.