Hjärtevägg is a word I should remember, it sounds nice. Usually, it's called hjärtvägg. Unfortunately, the floor plan is not enough to say anything for sure. If the upper floor is furnished, you can expect that an opening must be replaced with a beam of some sort, which doesn't need to be an insurmountable cost. If the upper floor is just an attic, it might work without reinforcement if the truss is self-supporting. You need to see a sectional drawing to be able to determine that.