Fig 3. DADs induced by Ca²⁺ overload during 1 Hz pacing under β-adrenergic stimulation in the myocyte model.

(a) Sub-threshold DADs (red arrows) and triggered APs (blue arrows) in between paced APs. Inset illustrates how the first DAD occurred just prior to the next stimulus. (b) Spontaneous [Ca²⁺]_i transients caused by underlying Ca²⁺ waves. Dotted lines indicate diastolic [Ca²⁺]_i. (c) Average [Ca²⁺]_JSR. Dotted lines indicate threshold for Ca²⁺ overload that resulted in spontaneous Ca²⁺ waves. This threshold decreased over the course of the protocol due to increased RyR sensitivity, increased [Na⁺]_i, and elevated diastolic [Ca²⁺]_i.