In Bridge Play, What is Meant by "Combining Your Chances?"
You have two ways of making your sixth trick given this ending.  You can find the outstanding hearts divided 3-3, or you can find the spade Queen onside.

The beauty is that you can take both chances.  First, play the hearts.  If they break 3-3 (or somebody has done some lousy discarding in the build up to this end position), you're set for your sixth trick with your baby heart.  If they do not break, you can then play the Ace of Spades (in case somebody has the singleton Queen), and finesse the Jack.

Your chance of success now are the 36% chance the hearts split, and the 50% of the time that the Spade Queen is onside in the case that the hearts do not break, or:

36% + (50%) * (64%) = 68%


Note that you have to start with the Hearts.  Testing the hearts does not result in the loss of a trick, it only establishes a trick for the opponents if the suit does not break.  Testing the Spade finesse will lose a trick if it is not correct.