Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
a light-headed feeling, like you might pass out;
worsening angina pain;
fast or slow heart rate; or
pounding heartbeats or fluttering in your chest.
Isosorbide dinitrate can cause severe headaches. These headaches may gradually become less severe as you continue to use nitroglycerin. Do not stop taking  isosorbide dinitrate to avoid headaches. Ask your doctor before using any headache pain medication.
Common side effects may be more likely to occur, such as:
headache; or
flushing (warmth, redness, or tingly feeling).
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Isosorbide dinitrate side effects (more detail)
