Digitoxin is a cardiac glycoside that has been found in Digitalis and has diverse biological activities.^1,2,3,4,5 It inhibits human recombinant α1β1, α2β2, and α3β1 subunit-containing Na+/K+-ATPases with Ki values of 250, 63, and 136 nM, respectively.¹ Digitoxin inhibits the human-ether-a-go-go (hERG) potassium channel, also known as Kv11.1, in HEK293 cells expressing hERG (IC50 = 11.1 nM).² It enhances developed tension and contractile force in electrically stimulated isolated guinea pig left atrial muscle when used at concentrations of 0.2 and 0.4 µM, respectively.³ Dietary administration of digitoxin (~1 mg/kg per day) attenuates congestive heart failure and reduces myocardial hypertrophy in a rat model of myocardial infarction induced by coronary artery ligation.⁴ Digitoxin is also cytotoxic to a panel of 10 human cancer cell lines, including myeloma, lymphoma, and leukemia cancer cells, with IC50 values ranging from 12 to 76 nM.⁵ Formulations containing digitoxin have previously been used in the treatment of congestive heart failure and cardiac arrhythmias.