Heatbeat felt under my sternum after cardio exercise?

Hi!  I am a 26 yr old female, in shape.  I jog, mountain bike and am completing P90x at this time.

Recently, while mountain biking and doing the cardio aspect of P90x, my heart feels like it is beating too hard.  I can feel it under my sternum and it makes me nauseaus.  I have to take off what ever I am wearing because any pressure on that area makes it feel worse.

About 6 years ago I had an EKG while in the ER during an unrelated visit and my heart skipped a beat every so often.

Any ideas what this could be?  Thanks so much for your help.

[Jerry_NJ]

From what you say I assume you are familiar with your normal heart rate and take some time to warm-up before doing strenuous physical activity.  I don't know what a P90x is assume here too you know what to expect from past experience and you are getting a different heart reaction from normal.  

Your symptoms don't raise any real alarm in my mind, but you know what is normal and what isn't for you. So, it seems to me it would be a good idea to discuss with you primary care doctor, maybe it is time for a physical check up and you can add this to your inputs to the doctor.

Most of us have an extra or missing heart beat from time-to-time, but the nausea does seem unusual and the sensitivity for what you are wearing seems strange to me too. A good check up with your doctor may be the best plan.

[PitBullSupporter]

Thanks so much.  I think I'll make an appointment.  =)