The standard Heavy Cavalry's default behavior is to seek and destroy defenses. With a large amount of hitpoints, they can endure more than any other troop of their Age, as well as dealing a lot of damage before falling. However, their disadvantages is that they have low damage and can be killed easily by Anti-Heavy Cavalry Towers such as Ballista Towers, Cannon Towers, and Anti-Tank Guns and that they can only deal 30% of their regular damage against resource buildings.
The French unique Heavy Cavalry unit have 15% more damage and 20% more hitpoints than the standard Heavy Cavalry.
From the v3.0 update, The Greek unique Heavy Cavalry unit increased additional damage to 25% (previously 20%) and reduced additional HP to 10% (previously 15%). The data in the table has been modified.
Heavy Cavalry have a lot of health but are slow and have low attack power, so use them in groups.
Heavy Cavalry are weak against many defenses grouped together.
When pushing for trophies, you would need to destroy the Town Center. In many bases, the Town Center is in the center of the base. First, train up an army of Heavy Cavalry and a Wall Breacher. When attacking, deploy your Veteran Wall Sapper and wait till it destroys the necessary Walls. Then, deploy all your Heavy Cavalry in the areas which the Town Center closest to. If there are a few defenses blocking the way, destroy them. Then rally your Heavy Cavalry to destroy the Town Center.
Heavy Cavalry ignore defensive troops and pursue their targets, which are defensive buildings. However, if a defensive troop attacks the Heavy Cavalry, the Heavy Cavalry will attack back until the defensive troop is killed; thus making the Heavy Cavalry distracted. Try to use and deploy Ranged Infantry or Heavy Infantry after deploying the Heavy Cavalry to eliminate the defensive troops.
When fighting on defense, they have high advantages over range infantries and siege weapons but are slightly weaker when facing a heavy infantry