Persons who are physically active may have a lower pulse.
The possible causes of lightheadness is anemia
(low blood count), arrhymthmia ( abnormal rhymth of the heart), low blood glucose
, problems related to the inner ear
,decrease blood pressure, dehydration
, side effect of medication.
You should consider revisiting your cardiologist
who may perform investigations to rule out cardiac disease and also check for the other causes.
In terms of the heart burn-reflux can be related to diet (use of fatty,spicy, acidic foods), medication (such as nsaids), bacteria (helicobacter pylori can cause ulcers)
In most persons lifestyle changes are recommended first , if not effective then medication can be used.
Lifestyle changes would involve reducing intake of the foods mentioned, reducing carbonated drinks, weight loss if overweight, using small meals, waiting at least 2 hours before laying down after a meal.
There are different medications available : antiacids, histamine blockers, proton pump inhibitors.
I hope this helps