Welcome to Healthcaremagic,Chest tightness
or chest pain
are very uncommon side effects for proton pump
inhibitors (Nexium) and although these may be there for the anti histamines
used against allergy
still are not reported for the antihistamines used against acidity (rantac).
Still if the rest of medical check ups has ruled out any other causes specially related to heart then perhaps the cause for his issues are with the medications listed.
So the best things to do at this place in time would be to inform your doctor of the issues that you have faced with the use of the medications for acidity. He/she may try a different proton pump inhibitor or a different H2 receptor antagonist or he/she even has the option for prescribing antacids for controlling the acidity issues. Besides that diets high in fiber may also hep with the acidity issues.
Hope This was helpful :)
Please Let me know if you further inquiries