Disclosed is a method for culturing myocardium-resident cardiac progenitor cells, comprising: embedding myocardial fragments into hydrogel; culturing the myocardial fragment into hydrogel; degrading only the hydrogel to recover cardiac progenitor cells grown out of the myocardial fragment to the hydrogel; and amplifying the cardiac progenitor cells in vitro. Also, the cardiac progenitor cells, a method for differentiating the same, and the use thereof as cell therapeutic agent for heart diseases are provided. In addition to possessing the potential to differentiate into cardiomyocytes, osteoblasts, adipocytes, chondrocytes, vascular endothelial cells, smooth muscle cells, neural cells, and skeletal muscle cells, the myocardium-resident cardiac progenitor cells can spontaneously differentiate into cardiomyocytes even in the absence of a special differentiation inducing agent. Thus, the cardiac progenitor cells can be used to produce bio-active medicines such as cell therapeutics and tissue engineering therapeutics with high industrial applicability.