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After myocardial infarction (MI), the noninfarcted myocardium undergoes significant hypertrophy as part of the post-MI structural remodeling. Electrophysiological changes associated with the hypertrophied remodeled myocardium may play a key role in arrhythmia generation in the post-MI heart. We investigated the cellular and ionic basis of arrhythmias in remodeled left ventricular (LV) myocardium 3 to 4 weeks after MI in the rat. We analyzed (1) the incidence of induced ventricular tachyarrhythmias (VTs) in the in vivo heart, (2) action potential characteristics and arrhythmia mechanisms in multicellular preparations and isolated remodeled LV myocytes, and (3) the density and kinetics of the L-type Ca²⁺ current (I_Ca-L) and the fast and slow components of transient outward K⁺ currents (I_to-f and I_to-s, respectively). The results were compared with those from sham-operated rats. In vivo, programmed stimulation …