PROBLEM TO BE SOLVED: To provide a therapeutic and preventive medicines for heart failure which are not accompanied by genetic manipulation or gene expression, by providing a phospholamban-binding substance, and a therapeutic medicine and a preventive medicine for heart failure, which correct abnormality in the dynamic state of Cain myocardial cells in which the substance exists.SOLUTION: By the use of a fusion protein including the cytoplasmic domain of phospholamban as a target, a phospholamban-targeted modified mRNA aptamer is identified with the SELEX method. The aptamer, its deletion mutant, and the like, is found to possess the stability in blood, and, by binding to phospholamban to release suppression of the SERCA activity of the phospholamban, and to enhance the SERCA (Capump ATPase of the cardiac sarcoplasmic reticulum) activity, and to enhance the contraction and relaxation capacity of myocardial cells. The phospholamban-modified mRNA aptamer can be used as a therapeutic and preventive medicines for heart failure.
