Digoxin is a cardiac glycoside extracted from the foxglove plant, digitalis. It is widely used in the treatment of various heart conditions, namely atrial fibrillation, atrial flutter and congestive heart failure that cannot be controlled by other medication. Digoxin preparations are commonly marketed under the trade name Lanoxin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. (From Martindale, The Extra Pharmacopoeia, 30th ed, p666) Digoxin is a cardiotonic glycoside obtained mainly from Digitalis lanata; It consists of three sugars and the aglycone digoxigenin. Digoxin binds to a site on the extracellular aspect of the of the Na+/K+ ATPase pump in the membranes of heart cells (myocytes). This causes an increase in the level of sodium ions in the myocytes, which then leads to a rise in the level of calcium ions. The proposed mechanism is the following: inhibition of the Na+/K+ pump leads to increased Na+ levels, which in turn slows down the extrusion of Ca2+ via the Na+/Ca2+ exchange pump. Increased amounts of Ca2+ are then stored in the sarcoplasmic reticulum and released by each action potential, which is unchanged by digoxin. This is a different mechanism from that of catecholamines. Owing to its narrow therapeutic index (the margin between effectiveness and toxicity), side effects of digoxin are inevitable. Nausea, vomiting and GIT upset are common, especially in higher doses. Decreased conduction in the AV node can lead to AV blocks, increased intracellular Ca2+ causes a type of arrhythmia called bigeminy (coupled beats), eventually ventricular tachycardia or fibrillation. An often described but rarely seen side effect of digoxin is a disturbance of color vision (mostly yellow and green color) called xanthopsia.