Cardiac glycosides (CGs) or cardiotonic steroids, which constitute a group of naturally occurring compounds with a steroid-like structure, can act on Na+/K+-ATPase as a receptor and activate intracellular signaling messengers leading to a variety of cellular responses. Epidemiological studies have revealed that CGs, used for the treatment of cardiac disorders, may also be beneficial as anti-cancer agents. CGs, acting in combination with other chemotherapeutic agents, may significantly alter their efficiency in relation to cancer cell elimination, causing both sensitization and an increase in cancer cell death, and in some cases resistance to chemotherapy. Here we show the ability of CGs to modulate apoptotic response to conventionally used anti-cancer drugs. In combination with etoposide, CGs digoxin may enhance cytotoxic potential, thereby allowing the chemotherapeutic dose to be decreased and minimizing toxicity and adverse reactions. Mechanisms behind this event are discussed.