What ion is necessary for cardiac contraction to occur?

The correct answer is Ca2+

Explanation:

Calcium ions are the ones which are necessary for the contraction of the cardiac muscle. The electrical impulses generated due to the cardiac action potentials cause the opening of calcium channels in the sarcolemma and sarcoplasmic reticulum, which causes calcium ions to leak into the muscle cell. This leads to a cascade of events that results in the contraction of the muscle.