Do not feed beef heart. Think of the natural menu of an arowana. Beef-heart is red meat. Are they eating cows in the wild? I think not. It also fouls up the water. As for being a good source of nutrition for them, it might be in small amounts, but there are other things (like prawns, krill, any kind of shrimp) that are MUCH better. And being good for growth, that I don't understand. I don't think I've ever heard of people suggesting foods to get arowanas to grow faster, and that is because there is no need. If a young arowana is fed well, it will grow easily 2-3" in a month.