When an organ’s activity increases, its oxygen requirements go up, and so does its need for blood. If narrowed arteries cannot widen to accommodate this need, or if for some reason they go into tight spasm that further restricts flow, the organ’s demands are not met, and it rapidly becomes ischemic. In pain and anger, the heart screams out a warning, and continues to do so until its shrieking exhortations for more blood are met, usually by the natural stratagem of the victim, who—alarmed by the distress within his chest—slows or stops the activity that is tormenting his cardiac muscle.
