AHU377-d is intended for use as an internal standard for the quantification of AHU377 by GC- or LC-MS. AHU377 is a methyl ester prodrug form of the neprilysin inhibitor LBQ657 . It increases plasma levels of atrial natriuretic factor (ANF) in conscious rats and anesthetized dogs when administered at doses of 10 and 30 mg/kg, respectively. AHU377 (30 mg/kg) increases ANF-induced urinary sodium excretion in anesthetized rats. Formulations containing AHU377 in combination with valsartan have been used in the treatment of mild to moderate hypertension and chronic heart failure.