Which Statement Is NOT True Regarding Cardiac Muscle

Which statement is NOT true regarding cardiac muscle?

A) Cardiac muscle cells must obey the all-or-none law of contraction.
B) Cardiac muscle cells rely on a sarcoplasmic reticulum for storage of Ca²⁺ ions.
C) Calcium-induced calcium release is the process by which extracellular Ca²⁺ triggers the release of stored Ca²⁺ from the sarcoplasmic reticulum.
D) Intercalated disks contain both desmosomes for firm attachment and gap junctions to allow communication.
E) The oxygen demand of cardiac muscle cells is high because they have many mitochondria.