Hypersensitivity to nitrates or nitrites. Low filling pressure, hypertrophic obstructive cardiomyopathy, constrictive pericarditis, cardiac tamponade, cardiogenic shock, circulatory collapse, aortic &/or mitral valve stenosis, severe hypotension (systolic BP <90 mmHg), head trauma & cerebral haemorrhage, increased ICP-associated diseases, marked anaemia, hypovolaemia, closed-angle glaucoma. Concomitant use w/ phosphodiesterase-5 inhibitors eg, sildenafil, tadalafil, vardenafil; soluble guanylate cyclase stimulator eg, riociguat.