I spent all of 30 seconds vetting that information, alologies. Here are the two article titles I am basing that off. Should have said protective against cardiotoxicity in some specific circumstances, maybe. Didnt mean to imply it's heart healthy like cheerios and alcohol.

"Morphine is protective against doxorubicin-induced cardiotoxicity in rat" https://pubmed.ncbi.nlm.nih.gov/17988779/

"Morphine enhances doxorubicin-induced cardiotoxicity in the rat" https://pubmed.ncbi.nlm.nih.gov/24531975/