questions

[uber368]

I'm a 50 yr old male, my risk factors are being 50 pounds overweight..my cholesterol is good..I quit smoking last year after 30 years.

Slowly but surely I started having  episodes lasting maybe just a short time up to half a day at a time to where my chest  just doesn't feel right...it is hard to explain, i mean, it doesn't hurt, but it feels like i am just weak in the chest....and generally very lightheaded...spaced out..faint..whatever you want to call it.  The lightheaded feeling is always in conjunction with the "funny, weak feeling" in my chest..in my heartbeat.  It's almost feels as if my heart is very tired and wants to take a nap on me.
Sometimes I have a burning in my chest across a broad area, unlike heartburn (definitely not heartburn).

Plus another thing is, I tend to get near syncope easy when standing up, but I only get this symptom when I am symptomatic [with all the above]. and on top of that I will feel just generally lightheaded and 'woozey' pretty much constantly. I get quite nauseated too at times. My blood pressure is the same as always when I'm feeling like this, never low enough to cause symptoms anyway. Glucose and EKG normal during symptoms.

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[Cleveland Clinic]

The only test that I would recommend at this point would be a Holter or an event monitor to try to see what you heart rhythm does during these episodes.  Fortunately, I don't think that your problem is cardiac related at all.  I get at least 5 questions/week that pertain to your problem.  Most of the time we don't know what causes these symptoms.  Some believe that it may have to do with being overweight, others think that it's related to deconditioning.  As long as your stress test and echo are normal I don't think that you have significant CAD.  Of course that does not say anything about your risk of SCD (sudden cardiac death).  The fact that you had smoked in the past put you at risk for developing mild CAD and its complications, SCD being one of them.  (We don't test for mild CAD because our technology and resources don't allow us to do so.  However, it is mild and moderate CAD that causes most of SCD in the Western World)  At this point, however, the only way that we know of as far as prevention is concerned is through CAD risk factor modification.  That means eating healthy, exercising, losing weight, avoiding tobacco, controlling sugar, cholesterol and blood pressure.  If the event monitor does not reveal anything it would further support that there is no cardiac arrhythmia to explain your symptoms.  

[uber368]

However,  I can usually do cardio exercise at my usual target pulse of 150-155 and exercise doesn't dramatically make the symptoms worse, although they don't get better either...This is even if I start exercise while feeling weak in the heart and lightheaded.

I have already had a regular stress test, an echo at rest, and the standard lab tests including thyroid, liver, comprehensive metabolics, etc etc. and these were all normal.

I guess my questions are,  what can be causing this,  and, does the fact that I can exercise and it doesn't get severely worse...does this pretty much rule out a dangerous (aka cardiac) problem?   Do I need more tests, or a specialist?  what can be causing this?  
I am very concerned because I have heard that feeling chronically lightheaded may be a sign of an impending cardiac event, and the feeling in my chest doesn't help me get over this fear.