[Ultrastructural aspects in the development of the human heart. I. The cytoskeleton and motility of human embryonic myocardiocytes].

Electron microscopic investigations performed on heart tissue fragments from 12 human embryos. 8 to 15 weeks of age, showed that at the age of 8 weeks the myocardiocytes are poorly differentiated cells: they contain microfilaments of actin and myosin inserted on the cytoplasmic aspect of plasmalemma, a smooth endoplasmic reticulin and mitochondria, accounting for the early contraction. Gap junctions appear among myocardiocytes, confirming the myogenic theory of heart contractions. Within 10 to 15 weeks, actin and myosin myofilaments organize in sarcomeres. Eberth disks appear and numerous mitoses are to be seen.