This database is described in
Please cite this publication when referencing this material, and also include the standard citation for PhysioNet:
This database includes 22 half-hour ECG recordings of subjects who experienced episodes of sustained ventricular tachycardia, ventricular flutter, and ventricular fibrillation. The reference annotation (.atr) files contain only rhythm labels (no beat labels); see this note for a key.
Greenwald SD, Albrecht P, Moody GB, Mark RG. Estimating confidence limits for arrhythmia detector performance. Computers in Cardiology 1985; 12:383–386.