Hi there. Bradycardia ie low heart rate could be due to multiple causes leading to reduced electrical impulses through heart. Aging, heart problems like heart attack, ischemic heart disease, hypothyroidism, electrolyte imbalance, some medications like beta blockers, all these can cause Bradycardia. Get her
tsh done to rule out hypothyroidism and Get 2d echo done once to rule out heart abnormalities. Consult nearest cardiologist soon.