The purpose of pharmacokinetics of cardiac glycosides is to study the time courses of glycosides in biological fluids, tissues and excreta. The extent of accumulation of a given dose at uniform time intervals depends only from the overall elimination rate constant. By knowing the elimination rate constant the extent to which a cardiac glycoside would accumulate in the body following a fixed dosing regimen can be calculated. The higher accumulation in the central nervous system requires a much longer time. Therefore it may be assumed that the brain is a deep compartment for cardiac glycosides and this compartment cannot be detected by analysis of plasma glycoside concentrations. Central side effects of cardiac glycosides may occur at therapeutic plasma levels. In renal disease a lower maintenance dose of digoxin and methyldigoxin should be administered or the same dose less frequently. Digitoxin does not accumulate in patients with renal failure or in anuria since the extrarenal elimination of digitoxin is much higher compared to digoxin and methyldigoxin.