Rationale: Heart muscle contraction is  activated by a synchronized systolic Ca release from sarcoplasmic reticulum (SR) via Ca sparks.
<clarity> Rationale: Heart muscle contraction is  activated by a synchronized systolic Ca release from sarcoplasmic reticulum (SR) via Ca sparks.
Rationale: Heart muscle contraction is activated by a synchronized Ca release from sarcoplasmic reticulum (SR) via Ca sparks.