TL;DR: Push petrified Deadrocks into lava to create a path or get a Goron pendant.
There should be three Deadrocks in that room. Deadrocks turn into stone when you hit them and are invulnerable for some time in almost all Zelda titles where they appear.
However, in Cadence of Hyrule, you can still push them around when they transformed into statues. If you push a petrified Deadrock into lava, they will melt down into hot stone and therefore create a path.
So in order to get the heart piece, you need to push two Deadrocks into the lava, and in order to get the treasure chest, you need to push one Deadrock into the lava.
Exiting and re-entering the room will make all of the Deadrocks respawn, in the event that you have killed them all with bombs.
Alternatively, get the Zora Flippers from the Zora prince and the Goron Pendant from the Goron shop, as the former enables you to swim and the latter further allows you to swim in lava.