While I agree with the above on the beef heart needing to be a rare treat, I do think that with the wide variety of other frozen foods, if you simply added a vitamin mix such as Vita-Chem your fish would be fine and get whole nutrition. Also, adding a live food such was flightless fruit flies would also help towards whole nutrition. I am a strong believe of feeding whole, natural foods over processed ones, and as long as you are able to make sure they have all the needed vitamins you should be fine. Though I should also add that Vita-Chem can be hard to find and frequently needs to be ordered online.
Additionally, OldFishLady has a good home-made pellet recipe. I don't remember it atm, but I am sure someone else could post it.
If you do decide to buy pellets, NLS small fish formula seems to be the highest in protein and easiest to digest. It also is great that it is so small in case you end up with a particularly small or young betta.
One more very important thing: with the frozen foods, do not thaw and refreeze any portion of the food. This causes it to lose any nutrition it has. Once it has been thawed it can be kept in the refrigerator for about a day, then discard any uneaten portion.