This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
In ECG one small division measures: 
Select and explain. 
A. 0.04 sec, B. 0.4 sec, C. 0.02 sec, D. 0.1 sec
A: 0.04 sec
Answer: A: 0.04 sec 
Explanation: Ans: a (0.04 sec) Ref: Ganong, 22nd ed, p. 550In ECG one small duration measures 0.04 sec.ECG:PR interval -- 0.12 - 0.2 secQRS -- 0.08 -0.10 secQT interval -- 0.40 - 0.43 secProlonged PR interval:* Hyperkalemia* 1st degree heart block (abnormally prolonged PR)* 2nd degree Mobitz type 1 (gradual prolongation of PR interval with missing of a beat)Short PR interval:* Tachycardia* WPW syndromeAbsent P waves: Atrial fibrillationDelta waveJ wave / Osborn waveSine wave patternInverse tick: WPW syndrome: Hypothermia: Hyperkalaemia: Digoxin