Myocardial infarction induces pro-arrhythmogenic Ca²⁺ release. (A; top) Line-scan images of representative spontaneous Ca²⁺ wave release during diastole (top) in one ventricular myocyte from sham (left) or PMI (right) mice. (Bottom) Occurrence of Ca²⁺ waves expressed as percentage (bottom) in cells from sham mice (white bar; n = 22) and in cells from PMI mice (red bar; n = 24). (B; top) Line-scan image of one ventricular myocyte isolated from PMI mice during electric stimulation at 2 Hz and during isoproterenol application. Red lines indicate electrical stimulation, and violet arrows indicate spontaneous triggered activity during diastole. (Bottom) Occurrence of abnormal triggered activity in myocytes from sham (white bar; n = 10) or PMI (red bar; n = 13) mice, and in myocytes from sham or PMI mice in the presence of 1 µmol/liter isoproterenol (orange bar for sham, n = 10; crosshatched orange bar for PMI, n = 13). n = 3 hearts per group. **, P < 0.01; ***, P < 0.001 versus myocytes from sham mice; ^##, P < 0.01 versus myocytes from PMI mice.