Prevacid 24HR is a type of heartburn treatment called a “proton pump inhibitor,” or PPI for short. When you experience heartburn two or more times a week, it’s time for Prevacid 24HR. Just one Prevacid 24HR pill prevents the acid that causes heartburn for 24 hours. Prevacid 24HR starts working the day you take it, with some people experiencing complete relief of symptoms within 24 hours.