This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'For cardiac muscle, Vmax can be used as a measure or: \nSelect and explain. \nA. Excitability, B. Contractility, C. Rhythmicity, D. Conductivity', 'role': 'user'}, {'content': "Answer: B \nExplanation: In cardiac muscle Vmax is used as an independent index of cardiac contractility.The velocity of an unloaded contraction (Vmax) is determined by the physicochemical propeies unique to cardiac muscle and is therefore considered a measure of the inotropic state. However, because load always exists, Vmax must be extrapolated from the force-velocity curve. Ref: Hoit B.D., Walsh R.A. (2011). Chapter 5. Normal Physiology of the Cardiovascular System. In V. Fuster, R.A. Walsh, R.A. Harrington (Eds), Hurst's The Hea, 13e.", 'role': 'assistant'}]