Proguanylin, the 116-amino acid prohormone, is a bioactive form of human guanylin that acts on intestinal guanylate cyclase, thereby regulating intestinal fluid and elektrolyte transport through the second messenger, cyclic GMP (cGMP). The cGMP increase inhibits salt absorption and stimulates chloride secretion into the gut. This imbalance of ions is accompanied by a massive accumulation of water in the gut that gives rise to diarrhea and dehydratation characteristic of enterotoxin activity. Proguanylin is found in circulation and plays an endocrine role by regulating the function of tissues such as the kidney and liver. Proguanylin is a significant marker in renal insufficiency. Plasma levels of proguanylin increase in patients with chronic renal failure who were undergoing hemodialysis. Studies have shown, that serum levels of Proguanylin has rise in patients with Cohn syndrome therefore it could be used as a novel marker in diagnostic and therapy of cardiac failure.