40. male. exercise often. pvcs (on/off) for 20 yrs. occasionally when on treadmill i get jarring, very brief (1 sec) center chest pain. cardiac?

Probably non-cardiac: It is more likely to be due to tension on a muscle insertion on the rib. Does it occur with a similar level of exertion on an elliptical trainer? If it occurs with increasing frequency, then an exercise (stress) test will clarify the issue

Tough to say: Any chest pain with exertion should be further evaluated by a cardiologist. You may be "giving yourself a stress test" so to speak, but get a real Stress test on the Cardiologist's treadmill while strapped up to a heart monitor to rule out any cardiac issues. Best wishes.