Hi thanks for your question.
CCF is itself commonest cause of persistent cough
due lung congestion.Get yourself examined by your treating physician to rule out increase in the cardiac failure which might be responsible for persistent cough.Mucinex
DM contain guaifensin which is expectorant and dextromethorphin which is cough suppressant.You can continue this medicine,if it is giving you relief .
Hope this answers your question.