Here's what I did: I obtained more feats in the caverns, maxed out my hearts and used a "better swimmer" upgrade, made sure I was at full health when I got to the lava pit, then managed to only burn through 4 hearts before I was able to reach the ladder inside the lava. Still completely unfair.
There is also another area of Demonaica's Lair that requires at least a +15% jump bonus to get past, which would be fine if you knew that before slogging through two rooms full of hungry ghosts and giant shadow bats, only to be forced to take a poison pill or throw yourself on the thorns. I mean, 4.6 hearts per hit from multiple giant shadow bats with their ultra-fast projectiles while being chased by hungry ghosts? Give a guy a break.