This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Preload leads to 
Select and explain. 
A. Isovolumetric relaxation, B. Isovolumetric contraction, C. Peripheral resistance, D. Parasympathetic nervous system activation
B: Isovolumetric contraction
Answer: B: Isovolumetric contraction 
Explanation: The force of contraction of cardiac muscle depends on its preloading and its after loading. The initial phase of contraction is isometric; the elastic component in series with the contractile element is stretched and the tension increases until it is sufficient to lift the load. The tension at which load is lifted is the afterload. The muscle then contracts isotonically. In vivo preload is the degree to which myocardium is stretched before it contracts.Ref: Ganong&;s Review of medical physiology, 24th edition.Pg no. 547