OBJECTIVE To evaluate the efficacy of amiodarone in tachyarrhythmias occurring acutely, in patients with different nosological entities of the heart. METHODS A retrospective study. METHODS Emergency-room patients and ward-patients, in an Internal Medicine Department of a University Hospital. METHODS Sequential sample of 148 patients with acute tachyarrhythmias, 138 out of them supraventricular (atrial fibrillation--116 cases; paraoxysmal supraventricular tachycardia--14 cases, and atrial flutter--8 cases). METHODS 81 patients had been treated with amiodarone; 67 patients had received several other antiarrhythmic drugs. RESULTS A favourable result of antiarrhythmic treatment was achieved in 84% of the patients who received amiodarone and in only 57% of those having been treated with the other antiarrhythmic drugs (p less than 0.025). A clearly distinct benefit of amiodorone was seen in the subgroup of patients with mitral stenosis, when compared with the whole of the other treatments (p less than 0.001). Amiodarone results were also better than the other antiarrhythmic ones in hypertensive patients (p less than 0.05). There was no difference between amiodarone and the remaining compounds in patients suffering from ischaemic heart disease, congestive heart failure and chronic obstructive lung disease. No adverse side effects were verified is this short term treated sequence of patients. CONCLUSIONS Amiodarone seems, in this study, to be a very effective antiarrhythmic drug for the treatment of supraventricular tachyarrhythmias. Its efficacy was superior in cases where the underlying disease was mitral stenosis or arterial hypertension. So, effectiveness of the compound seems to depend on the nature of the subjacente cardiac disease. The short term tolerability has been excellent. However, the small number of patients studied claims for bigger scaled similar investigations.