Nitroglycerin molecule, computer model. This is a heart drug, chemical formula: C3.H5.N3.O9). Atoms (balls) are colour-coded: carbon (yellow), nitrogen (dark blue), oxygen (red) and hydrogen (grey). Nitroglycerin is used to treat angina pectoris, pain due to the constriction of coronary arteries. It works by relaxing the artery walls and allowing the arteries to expand. The drug is prescribed as a patch, an ointment, pills or as an oral spray. Nitroglycerin is also a very unstable liquid explosive that is used in dynamite. It is prepared by nitrating glycerin. The three nitrate groups (red and blue) are seen around the glycerin molecule (yellow and grey).