Some days, while just sitting, driving, or even laying watching TV, my heart rate is upper 80s-100. Then other days it s low 60s and 70s while doing same things, and on those days it takes much longer during excercise to even get my heart rate close to my aerobic target rate. After stopping excercise, my heartrate comes way back down within 2-3min while other days stays around 100 even for hours after excercising. Should any of this cause me concern? I m 43, 165lbs, 5 9 . Have always been athletic and active, though with ups and downs over time. Have lost a solid 45lbs in the last 3years through excercise and better diet .