Cell loss and collagen infiltration occur in the area of the sinus node, throughout the atria, the central fibrous body, and the cytoskeleton of the heart with increasing age. Changes are most marked in the area of the sinus node, with destruction of as many as 90% of cells by the age of 75 years. In the center of the sinus node, expression of the L-type calcium channel protein Cav1.2 responsible for the upstroke of the action potential and depolarization is also decreased with aging.[182]The correlation between pathology and sinus node function, however, is poor, and sinus node function is preserved in most elderly patients, although sinoatrial conduction is decreased. Collagen infiltration and fibrosis are of lesser magnitude in the area of the AV node and more marked in the left and right bundle branches. Conduction times through the AV node increase with aging, with the site of delay above the His bundle. Despite age-related collagen infiltration, His-Purkinje conduction …