Implantable systems, and methods for use therewith, are provided for monitoring myocardial stability based on a signal that is indicative of functioning of a patient's heart for a plurality of consecutive beats. Sample data is obtained that is representative of functioning of a patient's heart for a plurality of consecutive beats, wherein each beat has a corresponding cycle length that may differ from cycle lengths of other beats. Such sample data is adjusted so that cycle lengths of consecutive beats represented in the adjusted sample data are substantially equal. Myocardial stability is then monitored based on the adjusted sample data. Where the obtained sample data is representative of electrical functioning of the patient's heart, electrical stability can be monitored, e.g., by monitoring for electrical alternations. Where the obtained sample data is representative of mechanical functioning of the patient's heart, mechanical stability can be monitored, e.g., by monitoring for mechanical alternans.