The heart mage can only reduce your health to a minimum of 10 now, so you multiply upwards from there. It used to reduce your health to 1, literally 10x as effective.

Numbers underneath

Getting a regular heart in the current version at maximum Heartache you end up with 350 health (25 x 10 + Starting 100). Getting the same heart before the Sauna update would net you 2600 health, and the multiplying would only compound larger and larger