To obtain the subject new peptide comprising a cyclic depsipeptide having a specific amino acid sequence, having strong cardiotonic effect, antiarrhythmic action and vasodilation action, free from adverse effect of arrhythmia, etc., and useful as a medicine, etc., for treatment circulatory diseases.

This new cyclic depsipeptide is represented by formula I [R1a, R1b and R1c are each H or methyl; R2 and R4 are each a lower alkyl; R3 is a lower alkyl or an aralkyl; R5 and R6 are each H, a 1-8C alkyl or an aralkyl; A and B are each ethylene or a (substituted) methylene; X and Y are each O or N(R1d) (R1d is H or methyl), with the proviso that R2 and R1d of X and/or R4 and R1c together may form a nitrogen-containing heterocycle together with adjacent carbon atom and nitrogen atom] and useful as a cardiotonic agent, an antiarrhythmic agent, a vasodilator, etc. The peptide is obtained by reacting a proline derivative of formula II (Bzl is benzyl) with an oligopeptide of formula III (Z is benzyloxycarbonyl) and removing a terminal amino protecting group of the resultant peptide of formula IV and cyclizing the peptide.