What Could Cause A Cold Sensation In My Chest, Especially Early Morning And Late At Night, Despite Being On Heart Medication?

Hi, lm a 63 year old female living in Zimbabwe i have been diagnosed with a heart condition and was put on meds but l have a problem, l feel cold right in the chest, like l can feel it in the heart usually early in the morning and late at night. What causes this and how can l be helped ... Please assist?