The aim of this study was to explore the capability of isosorbide dinitrate (ISDN) infusion to quench the 'hot phase' of unstable angina, a real cardiological emergency. Fifteen patients consecutively admitted to CCU because of angina at rest, with at least 4 ischaemic attacks per day, resistant to the usual therapy with oral and/or topical nitrates and calcium-antagonists, were included in the study. During ischaemia the electrocardiogram showed ST-segment elevation in 7 patients, ST-segment depression in 4, an alternation of ST-segment elevation and depression in 3 and pseudonormalization of a basally negative T wave in 1 patient. History of exertional angina with variable degrees of effort was reported in 6 patients and 9 had an old myocardial infarction. Coronary arteriography performed in 10 patients showed a significant stenosis of 1, 2 and 3 vessels in 5, 2 and 3 patients, respectively. ISDN infusion was started at 1.0 mg h-1, and was increased stepwise when persistence of ischaemic episodes had to be faced. The mean dosage infused was 3.5 mg h-1 (range 1.00-12). The mean duration of intravenous therapy was 8.3 days (range 2-25). Eleven of the 15 patients (73%) showed an effective decrease in the number of ischaemic episodes during ISDN infusion, as assessed by regression and variance analysis. After discharge (mean follow-up 59 months, range 2-96), 7 patients were free from ischaemic attacks, 3 underwent coronary by-pass surgery, 2 complained of some attacks and 3 died (2 because of sudden death three years after this study). In conclusion, ISDN infusion--individually tailored for dosage and duration--can be effective in 'cooling down' the storm of ischaemic episodes in unstable angina. An effective intravenous therapy with nitrates can represent, in some patients, a temporal remedy on the way to elective coronary bypass surgery and/or towards elective PTCA. Furthermore, in a sizeable number of patients with unstable angina, this approach can attain a complete abolishment of the ischaemic attacks.