SN instructed patient / caregiver regarding Metoprolol Tartrate, which is in a group of drugs called beta - blockers. That is affect the heart and circulation ( blood flow through arteries and veins ). Metoprolol is used to treat angina ( chest pain ) and hypertension ( high blood pressure ). It is also used to treat or prevent heart attack. Call your doctor at once if you have any of these serious side effects: chest pain, pounding heartbeats or fluttering in your chest, feeling light - headed, fainting; feeling short of breath, even with mild exertion, swelling of your hands or feet, nausea, upper stomach pain, itching, loss of appetite, dark urine, clay - colored stools, jaundice ( yellowing of the skin or eyes ), easy bruising, unusual bleeding ( nose, mouth, vagina, or rectum ), purple or red pinpoint spots under your skin, wheezing, trouble breathing. Less serious side effects may include: dry mouth, constipation, heartburn, vomiting, diarrhea, headache, drowsiness, tired feeling, sleep problems ( insomnia ), or anxiety, nervousness. Do not suddenly stop taking metoprolol tartrate. Sharp chest pain, irregular heartbeat, and sometimes heart attack may occur if you suddenly stop metoprolol tartrate. The risk may be greater if you have certain types of heart disease. Tell your doctor or dentist that you take metoprolol tartrate before you receive any medical or dental care, emergency care or surgery.