Fig. 1

Spontaneously beating ACMs identified in culture. a Light microscopy of isolated CMDF cells (0 days; bar 15 µm) and beating ACM identified at 3 days culture (bar 25 µm), and phase contrast microscopy of beating ACMs cultured for 6 and 9 days (bar 50 µm). Arrowhead indicates surface bulge and arrows the edges of the projections of ACMs that adhered to the surface membrane of neighboring fibroblast-like cell. b Left panel the light microscopy of the ventricular myocyte fraction. Arrowheads indicate the small cells co-precipitated with the cardiomyocytes. Right panel the phase contrast image of ventricular myocyte fraction cultured in the same culture condition of CMDF cells for 5 days. Arrow, arrowhead, and asterisks indicate the beating ACM, surface bulge, and dead cardiomyocytes, respectively. Bar 50 µm