PROBLEM TO BE SOLVED : To provide NEP inhibitor prodrugs or NEP inhibitors or pharmaceutically acceptable salt thereof for treating, preventing or delaying progression of diseases characterized by atrial expansion or remodeling.SOLUTION : Disclosed herein is a NEP inhibitor prodrug N-(3-carboxy-1-oxopropyl)-(4S)-p-phenylphenylmethyl)-4-amino-(2R)-methylbutanoic acid ethylester or pharmaceutically acceptable salt thereof. Also disclosed is a NEP inhibitor N-(3-carboxy-1-oxopropyl)-(4S)-p-phenylphenylmethyl)-4-amino-(2R)-methylbutanoic acid or pharmaceutically acceptable salt thereof.SELECTED DRAWING : NoneCOPYRIGHT : (C)2019, JPO&INPIT