For one, awesome on being super beasty with the laps before and cardio after!
But onto Black Cat
Natural Caffeine, Cocoa Extract (Standarized to 25% Theobromine), Licorice Root (25% Extract), Naringin (98% Extract), 1,3-Dimethylamylamine, White Willow Bark (25% Extract), Bioperine (95-98% Piperine)
all thrown together equaling 1 gram.
Big problem with proprietary complexes is you cant see how much of each is in there, which means it may be hard to see the problem.
If its giving you that kind of heartburn, definitely stop it and I doubt there is anything else you can mix it with to calm it. There is something in there that does not mix with your stomach, there are certain supps I bought, it did something similar and I can never use. Have you had issues with any of those ingredients before??
I remember when Drive was booming some people could not deal with the forsolkin in their stomachs, but that could be overcame because it was stomach pain not heartburn.
As someone who has an ulcer(possibly from the last 3 years of hell, or maybe the last 4 years of on/off supplement addiction ) I avoid heartburn if its caused by a product. Getting your acid up for extended periods of time has too many negatives in my opinion.
As for energy there are many other products or ways. Try bringing a thermos of Hot water (tea pot hot if you know what I mean) and a couple bags of Green Tea(I use Honey Lemon Ginseng Green Tea by Private Selections, needs no sugar tastes amazing) and drink it on your breaks. Green tea gives me more of an energy boost than things like Monsters or Venoms. Plus it enhances the mind and focus, and is healthy in many ways.
In fact...I am going to brew some of my new "Gunpowder Green Tea" I never had, but it sounds interesting. I am an herbal tea fanatic, and honestly...stuff is amazing as energy boosters, standard health,mental alertness, even helps cure a few minor ills and aches.