For an upset stomach, feel better fast with Alka Seltzer® effervescent antacid/pain reliever. For the relief of heatburn, acid indigestion, and sour stomach when accompanied with headache or body aches and pains, upset stomach with headache from over-indulgence in food or drink, pain alone (headache or body and muscular aches and pains). Active ingredient (in each tablet): aspirin 325 mg., citric acid 1000 mg., sodium bicarbonate (heat treated) 1916 mg.