Microvolt T-wave alternant (microV-TWA) is a beat-to-beat fluctuation in the amplitude of T-wave at a microvolt level. The amount of variation is small, on the order of microvolts, so sensitive digital signal processing techniques are required to detect microV-TWA. The appearance of microV-TWA has been suggested as a predictor of susceptibility to lethal ventricular tachyarrhythmias, and sudden cardiac death in different patients' populations. During the last decade, theoretical, experimental and clinical research efforts have focused primarily on microV-TWA, examining its mechanisms and predictive value using time-invariant cutoff values. The cellular mechanisms involved are not well-defined and are the subject of this investigation. This review discusses the bench-to-bedside literature that, over decades, has linked alternans of repolarization in cellular, whole-heart, and human studies with spatial dispersion of repolarization, alternans of cellular action potential, and fluctuations in ionic currents, intracellular calcium regulation, role of the beta adrenergic receptors and connexins that may lead to ventricular arrhythmias. This review then provides a contemporary framework for the use of microV-TWA methods to enhance risk stratification for sudden cardiac death, identifying populations for whom microV-TWA is best established.