ISOSORBIDE MONONITRATE ER 30mg tablets are an extended-release formulation of isosorbide mononitrate. They are used to prevent and treat angina (chest pain) by relaxing and widening blood vessels, which improves blood flow and reduces the heart's workload. The extended-release (ER) formulation provides a prolonged effect, helping to manage symptoms over time. These tablets are typically taken once a day for long-term management.