Digoxin increases the strength and vigor of heart contractions, and is useful in the treatment of heart failure. It is extracted from the leaves of a plant called digitalis lanata. Digoxin increases the force of contraction of the muscle of the heart by inhibiting the activity of an enzyme (atpase) that controls movement of calcium, sodium and potassium into heart muscle. Calcium controls the force of contraction. Inhibiting atpase increases calcium in heart muscle and therefore increases the force of heart contractions. Digoxin also slows electrical conduction between the atria and the ventricles of the heart and is useful in treating abnormally rapid atrial rhythms such as atrial fibrillation, atrial flutter, and atrial tachycardia.