The SA node fibre vaguely resemble cardiac myocytes; however, they are thinner, squiggly and stain less intensely (on H&E) than cardiac myocytes.

Description of the micrograph - the follow things are seen:

• Cardiac myocytes of the right atrium are seen at the right/bottom.
• Nodal artery, a branch of the right coronary artery is seen in the centre - on lumen.
• Sinoatrial node surrounds the nodal artery and abuts the darker staining cardiac myocytes.
• Lumen of the right atrium is on the left (endothelial lining not seen).
• Epicardial apidose tissue is to the right of the SA node.
• Epicardial space is on the right of the image.
• Superior vena cava is at the top of the image.
• Adjacent to nodal tissue is a nerve; the SA node interacts with fibres from the vagus nerve.

• 
  High mag. image of the same SA node.
• 
  Low mag. image of the same SA node.