AVP and Hyponatremia: Hyponatraemia may exacerbate the vulnerability of the myocardium by altering cellular excitability and intracellular calcium handling, thus increasing susceptibility to stress-induced myocardial injury.2 In some cases, hyponatraemia is linked to the syndrome of inappropriate antidiuretic hormone (SIADH) secretion, which leads to hypoosmolar hyponatraemia due to excessive ADH release.