Illustration of the molecular structure of digitoxin, a cardiac glycoside (heart drug). Digitoxin can be used in the treatment and management of congestive cardiac insufficiency, arrhythmias and heart failure. It acts by slowing the heart rate whilst increasing the strength of each beat. Digitoxin has enduring toxic effects, so digoxin, a less toxic alternative, is generally used preferentially. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white) and oxygen (red).