A method of determining the susceptibility to ventricular arrhythmias in a subject, the method including determining a reserve of refractoriness (RoR) and a reserve of memory (RoM) and combining the reserve of refractoriness (RoR) and the reserve of memory (RoM) to produce a metric of stability-of-propagation reserve (SoPR) in the subject, a higher value of SoPR indicating lower susceptibility to ventricular arrhythmias in the subject. Systems and apparatus for carrying out the method are also described.