Which of the following is the best explanation for the reduction in heart rate with aging?

Question

Quizplus · Accepted Answer

The resting heart rate is only slightly reduced, in contrast to the maximum achievable heart rate during exercise, which shows a more marked reduction. These reductions are caused by loss of sinus node pacemaker cells (as much as 90% are lost by age 80) and by decreased myocardial responsiveness to beta-adrenergic stimulation.

Which of the Following Is the Best Explanation for the Reduction