Sounds like the infamous CRUD. If so, not to worry, hearts and wispy leafed tomatoes are more susceptible to this drying and crumbling of the older leaves. Once they get outside into natural sunlight they should be able to outgrow this. It's not totally clear what causes it or what if anything you should do about it.
Here is just one thread on CRUD
http://www.tomatoville.com/showthrea...highlight=CRUD
There are quite a few more threads, if you want to use the search function on the message board.