What is a dangerous heart rate for a 51 year old female at rest?

Resting HR: HR is usually between 60-90, 72 is best. we usually don't worry till < 45 or 40( may not perfuse enough) , as athletes may have HR in 50's, or higher than 100 ( 120-130 is really more worrisome(beating to fast to perfuse), 100 just tells us to evaluate why high) . Hypo/hyperthoridism affect HR, medications ( caffeine/alcohol/),POTS, cardiac issues, rare conditions like carcinoid/ f/u/ w/ doc,