Why Can't Tetany of the Heart Occur Under Normal Conditions

Multiple Choice

Why can't tetany of the heart occur under normal conditions?

A) There are no distinct motor units in the heart.
B) There is inadequate oxygen supply via the coronary circulation to metabolically support a sustained contraction.
C) The refractory period in cardiac muscle lasts almost as long as the duration of the resultant contraction.
D) The heart contracts with maximal force every beat so it is impossible to increase the strength of the cardiac contraction.