Table 1:

Adult cardiomyocyte benchmarking parameters and values.

Benchmarking parameters and corresponding values of adult cardiomyocyte/tissue
Structural Organization	• Rod-shaped with aligned, developed myofibrils • Binucleated163 • Sarcomere length: ~ 2.0 – 2.2 μm164,165 • Cardiomyocyte surface area: ~ 10,000–14,000 μm2 166 • T-tubules present • Mitochondria localized near sarcomere167 • Expression of adult ventricular CM-specific structural genes (i.e. MYH7, MYL2, TNNI3, etc.)
Mechanical Properties	• Tissue elastic modulus ~10 – 50 kPa168
Force	• Contractile stress: ~ 30 – 60 mN/mm2 169,170 • Positive force-frequency ratio
Electrophysiology	• Low to zero spontaneous contractions24,171 • Characteristic notch at the top of upstroke166 • Resting membrane potential: ~ −90 mV172 • Action potential amplitude: ~ 100–110 mV173 • Action potential duration: ~ 230–300 ms174 • Depolarization velocity: ~ 250– 300 V/s173 • Conduction velocity: ~ 30–100 cm/s25
Calcium Conduction	• Cytosolic Ca2+ concentration175:  ○ Resting ~100 nM  ○ Post SR calcium release ~1 μM • Mature sarcoplasmic reticulum function • Increased gene expression of calcium handling machinery CACNA1C, SCN5A, KCND3, KCNJ2, SLC8A, ATP2A2, CASQ2, RYR2, GJA1, PLN • Robust organization of calcium handling machinery
Metabolic Maturity	• Reliant mainly on fatty acid oxidation: >70%142,143 • Reduction in glycolysis: < 10% of total energy source142 • Mitochondrial volume: ~30% of cell volume24