I did the same with my first few bichirs I owned it works well but as doc said beef heart is not to be used long term!
What I always do with small fish like that is make beefheart a good part of the diet until they are a chunky 5"-6". Then take them off beefheart because it's not healthy as a long-term staple. With the beefheart I'd feed blood worms, brine shrimp, tilapia, pellets, etc.., the main part for me is just feed a good chunk of beefheart as IME beefheart really helps chunk a fish up and give it a couple inches of length when young.
