The variable contractile strength of the heart.
D001696:Biomechanical Phenomena; D002302:Cardiac Output; D004548:Elasticity; D004735:Energy Transfer; D006321:Heart / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology; D006706:Homeostasis; D006801:Humans; D009124:Muscle Proteins / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology
D009124:Muscle Proteins