Cardiac glycosides are a class of organic compounds that increase the output force of the heart and decrease its rate of contractions by inhibiting the cellular sodium-potassium ATPase pump.

[1] Their beneficial medical uses include treatments for congestive heart failure and cardiac arrhythmias; however, their relative toxicity prevents them from being widely used.

Cardenolides differ from bufadienolides due to the presence of an "enolide," a five-membered ring with a single double bond, at the lactone end.

[5] While compounds of both groups can be used to influence the cardiac output of the heart, cardenolides are more commonly used medicinally, primarily due to the widespread availability of the plants from which they are derived.

[1] The refractory period of the AV node is increased, so cardiac glycosides also function to decrease heart rate.

Medicinal treatments for this condition work primarily to counteract tachycardia or atrial fibrillation by slowing down heart rate, as done by cardiac glycosides.

[11] Nevertheless, due to questions of toxicity and dosage, cardiac glycosides have been replaced with synthetic drugs such as ACE inhibitors and beta blockers and are no longer used as the primary medical treatment for such conditions.

[11] From ancient times, humans have used cardiac-glycoside-containing plants and their crude extracts as arrow coatings, homicidal or suicidal aids, rat poisons, heart tonics, diuretics and emetics, primarily due to the toxic nature of these compounds.

These dysrhythmias are an effect of an influx of sodium and decrease of resting membrane potential threshold in cardiac muscle cells.