When the shape changes a calcium ion is let through the S.R. into the myofibril causing the filaments to get excited causing them to contract.    From Wordnik.com.  [CreationWiki - Recent changes [en]] Reference

Occasional myocytes in both ventricles showed hypereosinophilia and loss of myofibril structure without associated inflammation (changes regarded as agonal rather than representing intrinsic myocyte pathology).    From Wordnik.com.  [PLoS ONE Alerts: New Articles] Reference

At 36 weeks of age, Tg mice (the group in transition from hypertrophy to HF) show significant degenerative changes in cardiomyocytes, including swelling of mitochondria, disruption of the nuclear membrane, and absence of myofibril structure.    From Wordnik.com.  [Naturejobs - All Jobs] Reference

However, as the disease progresses, cardiomyocytes show deterioration in some mitochondrial as well as myofibril features, evidenced by swelling of mitochondria, misalignment of myofibril structure, and blurring as well as breakage of Z-lines.    From Wordnik.com.  [Naturejobs - All Jobs] Reference