[Morphology of the sick sinus node].

Normally functioning sino-atrial nodes have been compared with nodes of patients with sick sinus syndrome (SSS) in a study of 65 autopsy hearts. 40-50 numbered sections of each node in constant intervals were compared quantitatively by light microscope. The results were: 1. Sino-atrial nodes of patients with SSS and normally functioning nodes are of the same size. 2. In patients with SSS the sino-atrial node has a higher content of collagenous fibres. 3. Sino-atrial node and conduction system tend to become sick at the same time. 4. This study offers no clue as to the etiology of SSS, but ischemia can be ruled out as the cause in most cases.