Isosorbide 5-mononitrate (IS 5-MN) has favourable pharmacodynamic properties, such as the specific half-life (close to 5 h) and the bioavailability (100% after oral ingestion). The efficacy of IS 5-MN (20 mg t.i.d.) in the treatment of stable angina has been documented in previous studies. In the present acute study, two subsets of patients were evaluated: the first group consisted of 10 patients with coronary vasospasm in whom oral IS 5-MN was effective in preventing myocardial ischaemia due to an abrupt reduction in coronary blood flow; the second group regarded 8 patients with a mixed form of angina, where the responsible mechanism for ischaemia can be considered a combination of increased myocardial oxygen demand and reduction of coronary blood flow due to vasoconstriction of large vessels. In all these patients, IS 5-MN was able to protect against transient myocardial ischaemia induced by isometric test. In conclusion, from the data available in our studies, IS 5-MN appears to be a useful drug in anginal patients: the beneficial effect is likely based on its capability both to prevent the abnormal vasoconstriction of diseased coronary vessels and to reduce myocardial oxygen demand.