Ventricular fibrillation is generally regarded as being lethal unless promptly halted. There have been reports of self-terminating ventricular fibrillation, but similar events are described by some cardiologists as polymorphic ventricular tachycardia or even torsade de pointes. To examine how experienced cardiologists would diagnose such tachyarrhythmias, electrocardiograms of self-terminating ventricular tachyarrhythmias compatible with accepted definitions of ventricular fibrillation (rate > 300/min) were sent to 22 cardiologists. During the study period of 19 months, 2462 patients treated in a 10-bed coronary-care unit were monitored by use of a single bipolar chest lead. 45 (2%) had episodes of ventricular fibrillation that were terminated by direct current (DC) shock. 12 self-terminating tachyarrhythmias (duration 5.2-49.5 s) were recorded from 8 patients, 3 of whom also had sustained ventricular fibrillation terminated by DC shock. The cardiologists offered 264 diagnoses for the self-terminating events; 42 (15.9%) ventricular fibrillation, 99 (37.5%) polymorphic ventricular tachycardia, 98 (37.1%) torsade de pointes, and 25 (9.5%) "other". The cardiologists differed (p < 0.01) in their response patterns. The findings show that rapid self-terminating ventricular tachyarrhythmias are not uncommon in coronary-care unit patients, and that the diagnostic categorisation of these important events is highly subjective and inconsistent.