I noted an immediate decrease in resting and exercise heartrate, and a reduction in aerobic capacity. I have kept exercising
and now hardly notice the difference, except when I exercise
at altitude. I also initially experienced cold hands/feet, and very vivid dreams, both disappeared in time. No stomach upset or other problems.
Rapid heartbeat with a beta blocker is unusual, unless you're trying to wean yourself off of the drug. Discuss it with your cardiologist or PCP.