A nitrovasodilator is a pharmaceutical agent that causes vasodilation (widening of blood vessels) by donation of nitric oxide (NO),[1] and is mostly used for the treatment and prevention of angina pectoris.

Slow acting substances would hold the danger of ischaemia due to an uncontrollably low blood pressure and are therefore contraindicated.

Depending on the circumstances, even fast acting substances can be contraindicated – for example, glyceryl trinitrate in patients with obstructive heart failure.

[2] Occasionally, severe hypotension occurs shortly after beginning of treatment, possibly resulting in intensified angina symptoms or syncope, sometimes with bradycardia (slow heart rate).

[8][9] Nitrates exhibit development of tolerance, or more specifically tachyphylaxis, meaning that repeated application results in a fast decrease of effect, usually within 24 hours.

Newer theories include increase of oxidative stress resulting in deactivation of NO to peroxynitrite, and liberation of the vasoconstrictors angiotensin II and endothelin as the blood vessels' reaction to NO-mediated vasodilation.

Glyceryl trinitrate acts fast and short (10 to 30 minutes), while most other nitrates have a slower onset of action, but are effective for up to six hours.

[2] Nitroprusside, given intravenously, acts immediately, and after stopping the infusion blood pressure returns to its previous level within ten minutes.