In electrocardiography, T wave alternans (TWA) represents the phenomenon of oscillation of the shape and/or amplitude of the T wave from one heart beat to the next, and its origin is explained by two potential hypotheses. The first one talks about restitution of action potential duration, and the second one about calcium restitution. TWA shows dependence on frequency, temperature, circadian variations, but also activation of the autonomic nervous system (ANS). It is possible to influence the amplitude and prevent TWA with pharmacologic options or external mechanical action using transcutaneous electrical vagus nerve stimulation (TENS), spinal cord stimulation, or ICD shock delivery. Numerous electrophysiological studies have shown that repolarization alternans is an important indicator of cardiac electrical instability, and thus susceptibility to the development of ventricular tachyarrhythmia episodes (VTE) and sudden cardiac death (SCD). Timely detection of increased TWA from surface or intracardiac ECGs opens opportunities to develop new methods of warning and terminating arrhythmias by delivering electrical impulses or pharmacological substances via micro-electromechanical systems (MEMS) to prevent potential SCD. It is a death due to a cardiovascular cause that occurred within one hour of the onset of symptoms. Coronary artery disease is the most common cause of SCD, and is responsible for as many as 80% of all cases. In adult patients with structural heart disease, a positive MTWA during low-intensity exercise proved to be an effective marker of susceptibility to ventricular arrhythmias. The Fast Fourier Transform (FFT) is the most widely used spectral method for its evaluation. The prognostic utility of TWA is greatest in patients with ischemic heart disease, post-MI and non-ischemic cardiomyopathy, particularly when assessing and considering ICD candidates. A multifactorial model based on the strategy of simultaneously using multiple markers of different aspects of the electroanatomical substrate (CAD, LVEF and MTWA) provides a significantly more accurate risk prediction for SCD, therefore it makes a good choice for a rational, financially profitable decision to implant an ICD, and the one with the least complications for patients.