To provide a therapeutic and prophylactic agent for cardiac failure caused by myocardial diastolic dysfunction or left ventricular diastolic dysfunction, angina pectoris caused by diastolic coronary circulation dysfunction, and catecholamine-induced hypertension.

The therapeutic and prophylactic agent contains 1,4-benzothiazepine derivatives represented by general formula [1] wherein R1 represents hydrogen, or a 1-3C lower alkoxy group; R2 represents hydrogen, a 1-3C lower alkoxy group, a phenyl group (wherein the phenyl group may be substituted by 1-3 substituent(s) selected from the group consisting of a hydroxy group, and 1-3C lower alkoxy groups), or a group represented by general formula (A) (wherein R3 represents 1-3C acyl group); X represents -CO-, or -CH2-; and n represents 1, or 2.