Yes, for some this might happen. The heartburn or sore throat that you experience after eating chocolate is a result of reflux of some of the stomach contents into the throat. Chocolate, sometimes, causes this because it contains two heartburn-triggering substances. They’re theobromine and caffeine. And since, dark chocolate has a higher content of theobromine- and caffeine-containing cocoa solids than milk chocolate, 1 oz. of dark chocolate would have a more potent heartburn-causing effect than milk chocolate.