What term describes the ability of cardiac muscle to contract spontaneously without a stimulus?

• A. Automaticity
• B. Conductivity
• C. Excitability
• D. Contractility

Answer: (A)

Automaticity is the ability of cardiac muscle to generate an electrical impulse and contract without external stimulation. Specialized pacemaker cells in the sinoatrial node spontaneously depolarize to reach the threshold, initiating an action potential that spreads through the conduction system and triggers contraction. This intrinsic pacing keeps the heart beating in a regular rhythm even without neural input. Conductivity refers to the spread of impulses once generated, excitability is the ability to respond to a stimulus with an action potential, and contractility is the strength of the contraction itself. The concept described here specifically covers self-initiated electrical activity.