Diltiazem is considered, at normal doses, compatible with breastfeeding.
There are no published observations of disorders in infants caused by this substance, or damage to the breastfed itself.
From the limited available data, could be extrapolated that the amount ingested by an infant would be less than 1% of the administered to the mother, so it probably would not cause adverse reactions in children .
Warning of the manufacturer:
Diltiazem passes into breast milk so women treated with the drug should not breast feed their children.