Table 6.

Aging-induced cardiac perturbations.

Aging models	Ultrastructural changes	Quantitative TEM	References
Male Fisher 344 rats 6 and 26 months	↑ Cardiac autophagic vacuoles by caloric restriction in 26-month-old rat hearts	Mean fractional autophagic vesicle volume is increased from 0.7 to 1.4 by caloric restriction in 26-month-old rat heart	Wohlgemuth et al., 2007
Male mice 4–24 months	Dysregulation of gap junction and intercalated disc morphology	No	Bonda et al., 2016
Male mice 4 vs. 24 months	↓ Mitochondrial volume/myocyte (mi/myo), myofibrillar volume (mf/myo), ↑ sarcoplasm volume (sp/myo) by age, spermidine restore these changes to nearly 4 months level	Mi/myo from 0.35 to 0.28, mf/myo from 0.53 to 0.51, sp/myo from 0.10 to 0.19 from 4 to 24 months, spermidine restore these values	Eisenberg et al., 2016
Male mice 4–24 months	Elongated mitochondria, “megamitochondria,” in aged mice	Mitochondrial area increased from 0.6 to 1 μm2	Liang et al., 2020

Highlighted in bold font are the subcellular structures observed by TEM.