palpitations with chest pressure

For the past week I've had chest pressure behind my breastbone with palpitations.  What I've had done so far - labs, CXR, and EKG are WNL, though I've only seen my GP.  I will get set-up with a Holter today.  
Today for the first time I'm having some shortness of breath and slightly tachy (100-110) at rest with O2Sat above 96.
I don't know exactly how to describe it, but the sensation I feel in my chest is that either there is crowding of my organs.  It feels like something is pushing against my breastbone, and there is pressure in the left side of my chest.  I do not feel pain, occasionally it is uncomfortable, but it feels like there is either a foreign object making every crowded, or my organs are enlarged causing the sensation.
Any thoughts or suggestions?
Thanks.

[CCFCardio MD1]

If a patient presented with palpitations, shortness of breath, and chest pressure is concerning for cardiac causes, though the level of suspicion is based on the presence of risk factors (hypertension, cholesterol, family history, etc) and on more specific components of the chest pressure (is it constant for weeks at a time?).  It would not be unreasonable for certain patients to undergo further testing such as a stress test and Holter monitor.