The degree of temporo-spatial variation of repolarization during single (S2) and double (S3) premature stimulation was evaluated in five closed-chest anesthetized dogs. Monophasic action potentials (MAP) were simultaneously recorded with contact electrode and MAP duration (MAPD) restitution curves constructed from right ventricular (RV) and left ventricular (LV) endocardial sites. At a given coupling interval, S3 was associated with significantly greater dispersion of MAPD then S2 (spatial dispersion, i.e., between RV and LV). Similarly, at a given diastolic interval, S3 at RV and LV sites, was associated with significantly greater dispersion of MAPD then S2 (temporal dispersion). It is concluded that S3 is associated with greater temporo-spatial dispersion of repolarization then S2.