Is Increased Heart Beat Safe After Exercising?

My resting heart rate is normally about 68 or 70. I bicycled about 17 miles earlier today and had a hard time breathing and feeling like my heart was beating too fast. I haven't exercised regularly in the last two months. An hour after the ride my pulse was 93 and still seems to be beating too fast. However my blood pressure was normal---117 over 70. Should I be concerned? This also happened to be earlier this week while I was walking briskly up a hill. I am 64 years old; weight 134 and otherwise in excellent health.