If you're looking to farm XP and Diablo 4 Gold quickly and collect Malignant Hearts efficiently in Diablo 4's season one, the strategy revolves around repeatedly farming the DinDai Hollow Malignant Tunnel. This method grants a good amount of XP and Malignant Hearts per hour. However, let's dive into more details and best practices for this strategy.

Requirements
This strategy can only be done in Season 1 and relies on the new season content, which includes Malignant Tunnels scattered throughout the world map.

Malignant Hearts
Malignant Hearts are seasonal items that you can insert into jewelry sockets. There are 32 different hearts, some of which can significantly empower your build. Additionally, you can break down unwanted hearts to craft more powerful ones at Corman's workbench.

Wrathful Hearts
Among the Malignant Hearts, Wrathful Hearts (also known as Black Hearts) are the most challenging to obtain due to their rarity. To optimize your chances of getting them, you need to run as many Malignant Tunnels as possible.
Malignant Tunnels: These tunnels offer both good XP and a chance to encounter Elite monsters, which drop Malignant Hearts when defeated.

Efficient farming
To maximize your farming efficiency, follow these steps:
Run the Dinh Day Hollow Malignant Tunnel, as it offers the best XP per hour.
During your run, you will encounter Champions that drop Malignant Hearts when defeated.
After killing a Malignant monster, a heart will appear, and the monster will respawn after a short delay.
Click the heart to start the respawn process, then move on and clear other areas.
Once you complete your circuit, the remaining straggler monsters, including Malignant monsters, will teleport to you.
This allows you to kill the monsters efficiently and avoid waiting for respawns.

Resetting the dungeon
To reset the dungeon quickly, follow these steps:
Click "Exit Dungeon" and then "Exit Game" to leave the game.
Rejoin the game, and you'll be right outside the dungeon's exit.
Enter the dungeon again, and it will have reset.

Other options:
If you want to mix things up or level even faster, you can consider the following options:
Farm strongholds in World Tier 3, as it provides enhanced experience gains. Just clear an efficient route, ignoring the boss, and reset.
Participate in Legion Events for high-density monster kills. Use a tracker to know when they'll spawn, and arrive a couple of minutes early to build up the XP buff.

Conclusion:
With the strategy of farming DinDai Hollow Malignant Tunnel, you can efficiently collect both XP and Malignant Hearts in Diablo 4's season one. Remember to maximize your XP gains by using the trick to reduce waiting time for monster respawns. Happy hunting, and enjoy your adventure in the dark world of Diablo!