I Noticed An 'odd' Heartbeat A Couple Weeks Ago After

I noticed an 'odd' heartbeat a couple weeks ago after rather strenuous aerobic exercise that I had not done for several months. It had not happened before. Using a stethoscope I listened to my heartbeat and heard something like this: 3 beats, pause, 6 beats, pause, 9 beats, pause, 4 beats, pause, and so on. I have no chest pains, dizziness, or other symptoms, but when it happens, I can actually feel my heart beat in my throat, if that makes sense. I'm 62 and take meds for high blood pressure (keeps it around 125/80), Lipitor, and some for bi-polar. I've also been diagnosed as a Type II Diabetic with an AIC under 6.0. I am not a smoker or drinker, but do like coffee, which I think I'm going to have to give up. Things seem to settle down with rest, and I'm fine when I get up in the morning. Lots of activity and stress seem to set it off. Your opinion? (Mary)
Thanks.