Digoxin is a commonly used drug in the management of Congestive heart failure and Supraventricular tachycardia. Increased sensitivity to Digoxin is noted in states of Hypokalemia, Hypomagnesemia and Hypercalcemia making establishment of true therapeutic concentration difficult because all parameters are interactive. There is a difference between peak plasma concentration and peak tissue concentration of Digoxin. Clinically effective range for Digoxin is not determined at the peak plasma concentration ( 2- 3 hours after oral dose), but rather at the time of peak tissue concentration ( 6-8 hours after oral dose). To ensure a correlation between plasma and tissue concentrations the appropriate time to collect the specimen is 8 hours or more after the dose.