Blizzard has announced that it will end support for DX9 and 32-bit systems for Heroes of the Storm in the next coming months. This basically means that the game will only have access to the 64-bit version of the game, along with DirectX 11 or higher.
Blizzard also noted that while the 64-bit Heroes client might still be playable on some machines using DirectX 10, this may not be the case for all configurations, which is why it recommends that all its players upgrade to at least DirectX 11.
As Blizzard concluded:
“We apologize for any inconvenience this may cause. If you‘re not already using the 64-bit Heroes of the Storm client and DX11 or higher, we encourage you to consider making the switch prior to July of this year, which is when we aim to go live with the planned changes.”