An electrocardiogram (ECG) analyzing system for analyzing electrocardiogram (ECG) signals, the system including: a computing device including: a transformer for transforming an ECG signal into a time-frequency representation over a plurality of frequencies over a period of time; a calculator for calculating a magnitude of the time-frequency representation; an analyzer for analyzing a degree of clustering of a plurality of low-magnitude values in the time-frequency representation; and a diagnosing system for diagnosing whether ventricular fibrillation is present based on the degree of clustering.