Rennie Heartburn & Indigestion is an antacid treatment that works to neutralise excess stomach acid. These tablets can treat a number of conditions including heartburn, indigestion, trapped wind, and an upset stomach. Rennie Heartburn & Indigestion works quickly and effectively in two ways: 1. Antacids (calcium carbonate and magnesium carbonate)get to work within minutes, powerfully neutralising excess acid in the stomach. 2. Simeticone, a highly effective anti-foaming agent, causes the trapped air bubbles to combine and disperse, helping to eliminate the symptoms discreetly and without embarrassment.