A method and devices for timing the delivery of non-excitatory signals for modifying myocardial contractility of a portion of the heart. The method includes the steps of applying electrodes to a plurality of cardiac sites, sensing electrical activity in a first cardiac site through a first electrode for detecting a first electrical depolarization event within a beat cycle, sensing electrical activity in a second cardiac site through a second electrode for detecting a second electrical depolarization event within the beat cycle, and applying a non-excitatory signal to the heart at or near at least the second cardiac site through at least one of the electrodes in response to detecting the second electrical depolarization event within an alert window period. The alert window period starts at a first delay from the time of detection of the first electrical depolarization event and has a first duration. The applying of the non-excitatory signal is delayed from the time of detecting of the second electrical depolarization event. The method may include steps for reducing the probability of delivering of improperly timed non-excitatory signals due to electrical noise and/or ectopic beats and may also include steps for preventing delivery of multiple non-excitatory signals at or near the second cardiac site within a single cardiac beat cycle. Preferably, the first cardiac site is located about the right ventricle or the right atrium of the heart and the second cardiac site is located about the left ventricle of the heart. The devices may also be adapted for pacing the heart and/or for delivering defibrillation signals to the heart.
