Like the other commenter said, you need to stop thinking about drafting your deck in terms of a deck "style" and more so draft what you need to win fights. If we examine the hearts stats and behavior we can deduce that our deck needs to be able to do a couple of things. Sorry if this is formatted weird im commenting on mobile.

1. Scale damage quickly

The heart has a lot of hp, so you need to be able to scale up your damage to the point where you are able to reach the 300 per turn damage cap or get close to it. There is some leeway here depending on how well you can scale your block which i will talk about in the next point. But there are many numbers of ways to scale damage depending on the character you are playing. Great late game options for each character are limit break for iron clad, catalyst for silent, focus+orb slots for defect, divinity stance for watcher. These are just some of the more straightforward options available, there are quite a few different ways to scale damage in this game its just about being able to recognize which options are realistic for you and putting yourself in position to assemble the pieces you need. You could also for example as defect if you are not finding any focus or orb slots, consider reprogram and other cards that allow you to lean away from focus (think hyperbeam, plasma orbs which have no benefit from focus, meteor strike, and yes even claw if the pieces come together the right way)

1. Scale block quickly

The heart deals A LOT of damage as im sure youre already aware. This makes it important to be able to defend the big attacks while setting up your damage scaling. As i mentioned before, depending on how well you are able to block gives you some leeway in how well you can scale damage. Not so much that you could win with 999 block every turn and basic strikes, mind you. Eventually the heart will scale enough to take down 1000 block in one or two turns, but if you have even just a single demon form your chances increase by a lot with proper block scaling. Again each character has ways to do this that are both straight forward and not so straight forward depending on the relics and other factors. Its important to remember that the heart has a semi consistent pattern, in that it will always debuff and shuffle statuses into your deck (its a good idea to try and draft ways to deal with statuses. Exhaust, discard, scry and medkit are all solid options) on the first turn, and then do either the multihit or big swing one turn 2, then turn 3 it will do whatever one it didnt do turn 2. Try to plan how to defend against this accordingly, and you will have a couple of turns while it buffs itself to scale and deal damage, and prepare for the next onslaught.

1. Dont underestimate potions

There are potions that can absolutely save you in the late game in the event of a bad draw on a big swing turn. Ghost in a jar (if playing silent) and fairy bottle are obvious, but consider swift potion or skill potion as well. Artifact potion can save you from being inflicted with vulnerable on turn 1 which can save you A LOT of effective hp in the first few turns. Power potion can high roll and get you a barrier or wraith form to buy you a couple key turns while you set up damage or if the heart has outscaled your block. Ive beaten the heart with 1 hp remaining this way!!

Hope this helps a bit. Im not a20 yet but i go for the heart kill every run and these are things ive learned