A preparation of the dried leaves or seeds of the foxglove (Digitalis), used historically as a heart stimulant. Modern clinically prescribed drugs derived from digitalis include digoxin, which belongs to a class of drugs known as the cardiac glycosides. They are used to treat heart failure and some forms of arrhythmia because of their ability to increase the force of contraction of the heart muscle. Their toxic effects arise from their capacity to disturb the normal rhythm of the heart.