Heartburn, a burning sensation in the chest or throat, occurs in many patients when acidic stomach contents move into the esophagus from the stomach. This study will investigate the safety and efficacy of lansoprazole 15 mg once a day in treating frequent heartburn.

Inclusion Criteria:

1. Experiencing heartburn at least 2 days per week over the past month.
2. Having heartburn that responds to heartburn medication.
3. Be willing to discontinue the use of heartburn treatment for 7 days prior to inclusion in the study.

Exclusion Criteria:

1. Having history of erosive esophagitis or gastroesophageal reflux disease diagnosed by a physician and confirmed by testing (endoscopy).
2. Be unwilling to take only the study medication, and antacid provided as a rescue medication for relief of acute heartburn during the study.

Other protocol-defined inclusion or exclusion criteria may apply.