You can proceed to Heroic mode once you've completed all Chapters in Normal mode.
In Normal mode, shards are rewarded only after completing a Chapter for the first time.
The number of times you can finish a Chapter per day is not limited.

In Heroic mode, you can play each Chapter no more than 5 times per day, while the timer can be refreshed for gold.
Unlike Normal mode, in Heroic mode, hero shards are a reward that may drop with a chance on each playthrough.

Victories in Heroic and Normal modes will give you the following rewards which drop with a chance:
  • Experience;
  • Skill cubes;
  • Equipment items;
  • Hero shards;
  • Silver, Experience Potions, Memory Spheres.