Microtubule (MT) mechanotransduction links diastolic stretch to generation of NADPH oxidase 2 (NOX2)‐dependent reactive oxygen species (ROS), signals we term X‐ROS. While stretch‐elicited X‐ROS primes intracellular calcium (Ca²⁺) channels for synchronized activation in the healthy heart, the dysregulated excess in this pathway underscores asynchronous Ca²⁺ release and arrhythmia. Here, we expanded our existing computational models of Ca²⁺ signalling in heart to include MT‐dependent mechanotransduction through X‐ROS. Informed by new focused experimental tests to properly constrain our model, we quantify the role of X‐ROS on excitation–contraction coupling in healthy and pathological conditions. This approach allowed for a mechanistic investigation that revealed new insights into X‐ROS signalling in disease including changes in MT network density and post‐translational modifications (PTMs), elevated NOX2 expression, altered Ca²⁺ release dynamics (i.e. Ca²⁺ sparks and Ca²⁺ waves), how NOX2 is activated by and responds to stretch, and finally the degree to which normalizing X‐ROS can prevent Ca²⁺‐dependent arrhythmias.