Is there a connection between magnesium oxide and heart health.?

Yes, sometimes: If you have a proven low magnesium level, you need to improve the levels of magnesium in your blood before heart rhythm disturbances develop. Mag oxide helps correct levels. Remember, high magnesium levels in blood also cause heart rhythm disturbances, too. That's why you need not use mag oxide long term without known blood levels of magnesium level. Ok to use it short term for a week or so though.