As with other aura items such as Abyssal Mask, Frozen Heart's debuff can give away potential ganks.
Frozen Heart is an item best suited for tank champions because of the high amount of armor and ability haste but can also be useful for tanky support champions as both tend on be middle of enemy team during teamfights thus spreading the aura. Examples include Maokai, Amumu, Wukong and Sejuani.
The item also works well with champions that desire ability haste, have mana problems and make very good use of the passive for extra dueling potential. Examples include Warwick, Nasus, Udyr and Olaf.
Frozen Heart is sometimes not recommended on Rammus, as he relies on being hit with basic attacks in order to return damage to the enemy hitting him (particularly when a Bramble Vest or Thornmail is built). Since the frequency of this returned damage is reliant on the attacking unit's attack speed, Frozen Heart may inadvertently reduce Rammus' damage output slightly.
Frozen Heart is one of the few items to counter champions that function heavily around using basic attacks, such as Marksmen.