The present invention relates to a method for producing a cell population comprising myocardium-committed cells that differentiate into and survive as myocardial cells under a myocardial tissue environment. Specifically, the method is characterized in that adipose-tissue-derived multi-lineage/multi-potent progenitor cells are cultured in the presence of a polyamine. The present invention further relates to a cell population comprising the myocardium-committed cells, a cell preparation comprising the cell population, or a cell sheet. The present invention further relates to a method for treating a heart disease, which comprises administering the cell population to a subject.