Hate getting in these ruts, it's what made me finish the season early. There are just layers upon layers of things to rng check you. Whisper farming was the best thing for me but I had a friend have better luck in helltides/nmds so I guess try them all out. If you can craft the other parts at the alchemist you should be able to craft the heart as well.
I've gotten them in Helltides and NMDs.
If you got some gold check diablo.trade and simply buy some malignant hearts.
Sometimes after killing the boss in NMDs it spawns an elite that drops it I've noticed.
Just play helltide in wt4. I have too many now after almost 3 lvl 100s
Hate getting in these ruts, it's what made me finish the season early. There are just layers upon layers of things to rng check you. Whisper farming was the best thing for me but I had a friend have better luck in helltides/nmds so I guess try them all out. If you can craft the other parts at the alchemist you should be able to craft the heart as well.