The etiology of hyponatremia was congestive heart failure in 38 (28.8%) patients, syndrome of inappropriate antidiuretic hormone (ADH) secretion (SIADH) in 29 (22.0%) patients, gastrointestinal fluid loss in 24 (18.2%) patients, renal pathologies in 20 (15.2%) patients, the presence of drugs in 20 (15.2%) patients, and hypocortisolemia in one (0.8%) patient. This evidence concerns the gene AVP and congestive heart failure.