Single most impoant factor in control of automatic contractility of hea is:

D i.e. Sympathetic stimulation Intrinsic factor Length of activations - Most impoant factor Frank- starling law: "Energy of contraction is propoional to initial length of cardiac muscle fiber." Length of muscle fiber is propoionate to end diastolic blood volume (preload)Q. Extrinsic factor Adrenergc neural stimulation/ Sympathetic stimulationQ - Inotropic effect is smaller, Maximum in atria - It becomes impoant when the hea is increased as it permits adequate diastolic filling.