Cardiac tissue is an excitable and deformable medium in which tissue mechanics, cellular electrophysiology, and energetics are mutually coupled. Pathophysiological perturbations in coupling may result in electrical and mechanical dysynchrony, structural and functional remodelling of the cardiac substrate, which induce or exacerbate life-threatening arrhythmias and heart failure. Despite decades of research, the fundamental principles underlying electrical, mechanical, and energetic dynamics and self-organization that contribute to the onset and progression of arrhythmias and heart failure remain largely elusive.