This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiac Cycle, Subject name: Physiology
True about Bowditch's effect of hea 
Select and explain. 
A. Increased in HR decrease relaxation, B. Increased in HR increase relaxation, C. Increased in HR decrease contraction, D. Increased in HR increases contraction
D: Increased in HR increases contraction
Answer: D: Increased in HR increases contraction 
Explanation: Bowditch's effect: - Bowditch was a German physiologist. He put foh the term Treppe, which mean staircase. If you increase the frequency of a stimulus to a muscle, each succeeding contraction would be stronger than a preceding one. This effect has been c/a The staircase effect or Bowditch's effect. Increase frequency of stimulation results in increasing strength of contraction. Physiological basis for this effect is increased sarcoplasmic calcium. Strength of contraction of muscle [?] amount of sarcoplasmic calcium.