Nokea
What is the ability of cardiac cells to generate an electrical impulse without being stimulated by an external source?
Correct Answer: A
Rationale: Automaticity is the ability of cardiac cells to generate an electrical impulse spontaneously without external stimulation. It is a fundamental property of specialized cardiac cells like pacemaker cells. Contractility refers to the ability of muscle cells to contract in response to an electrical stimulus. Conductivity is the ability of cardiac cells to transmit electrical impulses. Refractoriness is the period during which cardiac cells are unable to respond to a new stimulus. Therefore, in this context, the correct answer is A: Automaticity.