High heart rate?

[Patrick]

While running hard (but not killing myself), I can get my heart rate to it's theoretical max (178) for my age (43). Once on a hot summers day my monitor showed 181 at the end of a hard run. 

But I feel fine, I had an ECG a year ago, and generally I am quite fit. 

Should I be worried?  Should I run easier? 

This is kind of a general question, not only about me personally.  For a person with high fitness level -- e.g. low resting pulse, daily aerobic training -- is the max heart rate usually higher than the traditional theoretical calculations? 

[Julian Downing]

I've always been a "high beater" and can still reach a higher max HRM than the theoretical calcuations would say I can do. Have always used HRM as a judgement of effort and fairly accurate predictor of finish time. In parallel one of my longstanding training partners (whose the same age as me) will produce the same effort @ -10 HR which supports the research that says were all individual and that the theortical calculations are just that - theory based on averages.

As you say, worth getting medically/lab tested though...