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
Myocardial  contractility  is  increased by: 
Select and explain. 
A. Atropine, B. Decreased end diastolic volume, C. Increased  heart  rate  from  70  to  150 beats/min, D. Reduced arterial pH to 7.3
C: Increased  heart  rate  from  70  to  150 beats/min
Answer: C: Increased  heart  rate  from  70  to  150 beats/min 
Explanation: Option A: Atropine is a muscarinic receptor antagonist that is used to inhibit the effects of excessive vagal activation on the heart, which is manifested as sinus bradycardia and AV nodal block. Effect on contractility is negligible. 
Option B: Decrease EDV decreases contractility by Frank Starling law.
Option  D:  Acidosis, hypercapnoea and hypoxia inhibit myocardium contractility.
Option C: This effect is known as Bowditch Effect (Myocardial tension increases with an increase in heart rate).