Endogenous cardiotonic steroids (CTS), also called digitalis-like factors, are a group of steroid hormones linking high salt intake and elevated blood pressure and in part responsible for target organ damage in arterial hypertension. CTS act primarily through their ability to inhibit the ubiquitous transport enzyme sodium-potassium adenosine triphosphatase (Na⁺/K⁺-ATPase). A portion of Na⁺/K⁺-ATPase does not seem to actively "pump" sodium and potassium but is closely associated with other key signaling proteins. Plasma concentration and urine excretion of CTS are increased in experimental models with volume expansion and on a high salt diet. Elevated plasma concentration of marinobufagenin has been shown in volume-expanded states such as essential hypertension, primary aldosteronism, chronic renal failure, congestive heart failure and pregnancy. In experimental models marinobufagenin induces heart and kidney fibrosis to the same extent as observed in uremia. Neutralization of marinobufagenin with antibodies prevents such heart remodeling. Expanding our understanding of this new class of hormones may lead to development of novel and effective therapeutic strategies in hypertensive patients with renal and cardiovascular complications.