An object of the present invention is to provide a novel method for sorting cardiomyocytes. Another object of the present invention is to provide a method for producing high-purity cardiomyocytes and a kit used therefor. The present invention provides a method for sorting cardiomyocytes, comprising a step of introducing miRNA-responsive mRNA into a cell group, wherein the miRNA-responsive mRNA consists of a sequence comprising the following (i) and (ii): (i) a nucleic acid specifically recognized by miRNA specifically expressed in cardiomyocytes, and (ii) a nucleic acid corresponding to the coding region of a gene, wherein translation of (ii) the nucleic acid corresponding to the coding region of a gene into protein is regulated by the nucleic acid sequence in (i) above, thereby achieving the aforementioned objects.