Behavior of human cardiac adipose tissue-derived stem cells (hcADSC) in culture. A, B) Bright-field micrographs illustrating morphology of the hcADSC cultures at passage 3 and 19, correspondingly. At early passage, cells maintain undifferentiated appearance and exhibit elongated, typical spindle-like shapes. At late passage, the cells increased in size and got flattened polygonal morphology. The cells were fixed with 4% PFA in PBS, and hematoxylin-eosin double stained; original magnification ×20. C, D) Transmission electron micrographs showing ultrastructure of hcADSCs at passages 3 and 19, correspondingly. At early passage, the hcADSCs exhibited morphological features characteristic of non-differentiated cells; their nucleus contained a small nucleolus (arrowhead) and scanty cytoplasm in which the cytoplasmic organelles were poorly developed. Arrows point to dilated cisternae of RER. Late passage hcADSCs showed large nucleus with prominent nucleolus (arrowhead) and cytoplasm filled with many cisternae of rough endoplasmic reticulum (double arrows). The presence of secretory-like dark granules (arrows) was noted. Scale bars equal 1 μm. Abbreviation: hcADSCs, human subepicardial adipose tissue-derived stem cells; PBS, phosphate buffered saline; PFA, paraformaldehyde, RER, rough endoplasmic reticulum.