I am 53 years old and have consistently exercised most of my adult life. Last year I briefly went into afib during a stress test. A follow up 30 day monitor showed seversl more additional brief afib episodes after briskly walking for 20 minutes or so. In the worst of them, I physically collapsed and my heart rate was recorded at 230 bpm. My cardiologist put me on a beta blocker and I bought the Alivecor ECG and a fancy running watch with chest strap to monitor my heart during exercise. A few months ago I slowly weaned off if the beta blockers and have continued to closely monitor my heart rate. I find that it jumps up quickly to between 140 and 160 bpm when I briskly walk and between 160 and 180 when I do a 2 mile bike ride on level ground. This occurs within a few minutes of setting out. i can't tell if I'm in afib but when I stop to check my pulse it generally feels regular (although it is pounding).. It is after exercising that I feel lightheaded or notice skipped beats and that it takes a good 30 minutes for my heart to generally calm down but when I check my Alivecor it generally says unclassified and only occasionally has shown me to be in afib. I downloaded the last 3months of data and plotted up to look for trends and saw that this is my pattern every day (I exercise 30 min/day). I'm wondering if others find their heart rate this high as well. I don't want to damage my heart and develop heart failure but also don't like taking drugs unnecessarily. Would like to get a better idea of how normal or abnormal this is...
Heart rate shoots up when exercising - Atrial Fibrillati...
Heart rate shoots up when exercising
These were exactly my first symptoms. Years before I was diagnosed with AF and Dilated Cardiomyopathy. The AF and high heart rate had damaged the heart. Personally I don't think you should have come off the BB, at least not without medical supervision. I am not a medic. Merely relaying my own experience.
Doesn't sound too good to me, your theoretical max heart rate is 167, you should only be up in the 170's during extreme exercise, unless you are extremely unfit, my heart rate is always about 20 beats higher than normal in first 10 or so minutes until whole body has warmed up, then it drops back to normal for rest of workout.
I'm pretty fit so is hard for me to relate, if I was you and hadn't been told to stop the beta blockers, I would be back on them until I talked to a cardiologist especially if I was going to keep exercising.
When I was on beta blockers and training, it sometimes stopped me from keeping up with the fast guys, but I always felt happier knowing that no matter how hard I went, my heart rate wasn't going to get outrageous and scare me 
How amazing you can get a THIRTY DAY monitor. I am having a 7 day one in a weeks time and getting it was like drawing hens teeth! Good luck with everything
Stephanietee
I do not think that this is not an uncommon experience as we age and not that abnormal. For what reason did you wean yourself off Beta Blockers? because they will keep your HR down but that of course may mean you can't exercise as vigorously - but isn't that the point?
Tachycardia may well be a pre cursor to arrythmia - believe me when I say if you can avoid AF through life style changes which may mean moderating your exercise regime, it will be much more advantageous to your long term health.
same here, i find i cannot do normal excersises i once did without the same thing happeneing. mowing the lawn puts me way high and will not calm down until after almost an hour of rest. weird. not pleasant. or even riding my bike............puzzling
i am interested in some feedback on your inquiry (following)
It would be nice to know a few things, such as your BMI, history of high blood pressure and smoking, and any hereditary heart or circulatory issues you might have. Your jumps in heart rate while exercising don't particularly concern me, but what makes me think of these things is your pulse of 140 when walking. Unless you're race-walking or going fast up steep hills, I can't imagine how it can get that high. I wonder if you might have an underlying circulatory problem that's manifesting in this way. It doesn't sound good.
I agree with Kodaska. I was experiencing many of the same symptoms as your self.They even gave me a stress test and that couldn't replicate the symptoms. A week later I was in the hospital having stents put in. Combo of circulatory issues and afib not a good thing. Eventually, I had to go to an EP who put me on the 30 day monitor and they found my afib. What I didn't know until later was that I was having episodes at night and it was really effecting my general well being. You need some answers if not for just your piece of mind.
I have a low BMI, have never smoked, normal to low blood pressure and rarely drink these days as I have figured out that drinking is a trigger for my tachycardia. Have always done moderate level exercise (no marathons for me! Just hiking and skiing and general active-type lifestyle) and the brisk walking I am doing is on flat level ground at a rate of 4 mph. Family history includes a father who had triple bypass a few years ago and a mother who has recently been found to be at high risk of congestive heart failure (high BNP test and abnormal nuclear stress test. Will have heart catheterization tomorrow to investigate further). That is what triggered my message here. When I saw my cardiologist last year he said that family history only mattered if the serious cardiac problems occurred before the age of 60. My grandfather died of a massive coronary in his 80's and my parents problems are occurring in their 70s so he didn't seen to regard any of that as relevant. I have always considered myself as very healthy and yet the heart rate jumping seems at odds with that and I don't want to ignore early signs that I could be headed in the same direction as my mother.
Afib caused by low heart rate? Ectopics when exercising.
Heart rate tracker anomalies 
Heart rate goes up with light exercise
