This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Digitalis, Subject name: Pharmacology
Digitalis does not increase which parameter of heart- 
Select and explain. 
A. Force of contraction, B. Myocordial contractility, C. Myocardial oxygen demand, D. Cardiac output
C: Myocardial oxygen demand
Answer: C: Myocardial oxygen demand 
Explanation: Ans. is 'c' i.e., Myocardial oxygen demand Effect of digitalis on hearto Main mechanism of action of digitalis is to increase in force of contraction of heart - a positive inotropic action.o Amongst given options, option d is the best choice - heart rate is decreased by digitalis and there is increase myocardial contractility without a propartionate increase in O2 consumption.How does digitalis decrease heart rate?# Heart rate is decreased by digitalis mainly in patients with CHF.# In CHF there is sympathetic overactivity and i vagal tone because of | CO2# Digitalis increases myocardial contractility (major action) - | CO and better emptying of ventricle - improvement in circulation - restoration of diminished vagal tone and abolish sympathetic overactivity - | Heart rate. Beside above main mechanism digitalis slows the heart rate by -A) Increased vagal tonei) Reflexly through nodosa ganglion.ii) Direct stimulation of vagal centre.iii) Sensitization of SA nodes to Ach.B) Extravagal - Direct depressant action on SA and AV nodes."The vagal action manifests early and can be blocked by atropine, whereas extravagal action becomes prominent later and cannot be reversed by atropine