The present invention relates to a method for producing a cell mass which contains a myocardium-committed cell capable of being differentiated and adhered as a myocardial cell under a myocardial tissue environment. Specifically, the method is characterized by culturing an adipose-tissue-originated multipotent progenitor cell in the presence of a polyamine. The present invention also relates to: a cell mass which contains a myocardium-committed cell； and a cell preparation or a cell sheet, which contains the cell mass. The present invention further relates to a method for treating a heart disease, which comprises administering the cell mass to a subject.
