Ultrastructural study of specialized conducting and working myocytes in the sinoatrial region of the human heart. I. Qualitative analysis

: A qualitative ultrastructural analysis of specialized conducting and working myocytes in the sinoatrial region of the human heart was made using autopsied and biopsied material from 45 men and women. Autopsied material was prepared not later as than 3 hours after the death. Biopsied material was taken during the operation for surgical correction of disturbances of cardiac rhythm and conduction. Cell contacts of light and dark myocytes within the sinus node, and of working myocytes of the right atrium were evaluated. The ratio of light to dark myocytes in the sinus node were estimated from both dead people and patients. The principles of correct ultrastructural classification of conducting and working myocytes in human heart are discussed.