The relationship of aging to histological changes in the conduction system of the normal human heart.

The effect of aging on histological changes of the conduction system was studied by serially sectioning 55 autopsied hearts weighing less than 300 Gm. None of the hearts showed evidence of cardiovascular disease nor were there any abnormalities in the clinical findings and ECG taken during the last 3 months of life. A reduction in the number of muscle cells and an increase in the number of collagen fibers were apparent in hearts taken from patients over 70 years of age. These findings were most evident in the S-A node and less so in A-V node, bundle of His, and left and right bundle branches. Deposition of amyloid substances was not observed in any portion of the conduction system.