Defense of the Heart deck

I've been planning a new casual deck for a couple weeks, and now that I finally have the cards in hand things are starting to take shape.  The basis of the deck is built around Defense of the Heart with the goal of fetching both Worldspine Wurm and Disciple of Bolas in order to draw 15 cards, gain 15 life, and be left with 3 5/5 wurm tokens (which are harder to remove than a single Worldspine Wurm).

Here is the deck as it stands after a few initial games of testing:

4 Deathrite Shaman
4 Veteran Explorer
3 Varchild's War-Riders
3 Disciple of Bolas
1 Woodfall Primus
2 Worldspine Wurm
4 Cabal Therapy
2 Concordant Crossroads
4 Gamble
3 Sylvan Library
1 Deathrender
4 Defense of the Heart
3 Natural Order
1 Badlands
3 Bayou
2 Bloodstained Mire
4 Forbidden Orchard
2 Forest
2 Mountain
2 Swamp
2 Taiga
4 Verdant Catacombs

Both Veteran Explorer and Deathrite Shaman can help speed up the deck and get Defense of the Heart into play around turn three, or either of them can be sacrificed to Natural Order.

Forbidden Orchard and Varchild's War-Riders are there to help give the opponent creatures in order to trigger Defense of the Heart.  If needed, Varchild's War-Riders can be sacrificed to either Disciple of Bolas or Cabal Therapy  once it has served its purpose.

Both Sylvan Library and Gamble are there to dig for any pieces that might be missing.  They've been working OK so far, though Gamble has been far better than Sylvan Library.  I'm considering switching out Sylvan Library for Sensei's Divining Top since I don't expect the game to go too long once I get the pieces that I'm missing.  I'd consider something else if there was a good replacement, and I've considered adding white for either Enlightened Tutor or Idyllic Tutor.

The copies of Concordant Crossroads are there so that I can swing with all of my creatures after Defense of the Heart has triggered.  Having drawn 15 cards should get either a Gamble or a Concordant Crossroads. 

The Deathrender is there mostly as a backup plan and is a good candidate to take out.  It's currently in there for testing, but has seemed too slow.  I don't completely want to rely on just Defense of the Heart or Natural Order, but turning to Sneak Attack doesn't work great since there aren't a lot of copies of the creatures and they need to be searched out of the library.

I'm not sure if it's worth working on a sideboard since I don't plan on playing this in tournaments.

Anyway, I thought that someone else out there might enjoy the deck or have some ideas on how to make it a bit better.  Let me know what you think.  It has been a lot of fun to play so far, though I'm sure that it can be improved.