Target 1 face-up "Elemental HERO" monster you control; halve its ATK until the end of this turn, but it can attack twice during this turn's Battle Phase.
These are some of the recommended Fusion Elemental HERO monsters to use Hero Heart on, because of their high base ATK power.
Zane Lvl 40 (Gate)
KC Cup Nov 2018 1st Stage
Inglorius Bastion Event
New Week Campaign!
The White Dragon of Legend
Train Your Kuriboh! Campaign
PvP Best decks
King of Game decks [Nov 2018]
KC Cup: 1st Stage [Nov 2018]
How to beat/farm Zane Lvl40 (Gate)
Masked HERO: deck recipe
Dragunity Synchro: deck recipe
Blue-Eyes Cosmo Brain: deck recipe
Amazoness: deck recipe
Gladiator Beasts: deck recipe
Geargia: Deck recipe [Jun 12 Updated]
Spellbook: deck recipe
Wall of Disruption | Deck and Rulings
Gozuki | Deck and Rulings
Destructotron | Decks and Ruling
Ancient Rules | Deck and Rulings
Floodgate Trap Hole | Decks and Ruling