What is the duration of the absolute refractory period in heart muscle?

The duration of the absolute refractory period in heart muscle is approximately 250 milliseconds. This physiological phase is crucial because it represents a time during which the cardiac muscle cells are unable to respond to a new stimulus, regardless of the strength of that stimulus. The absolute refractory period occurs after an action potential is initiated, during which the sodium channels are inactivated, making it impossible for another action potential to occur. This characteristic is vital for maintaining the rhythmic contractions of the heart and preventing conditions such as tetany, which can be detrimental to cardiac function.

The other durations presented in the answer choices do not align with the established understanding of cardiac physiology. For instance, 150 ms would be too short to allow for full recovery and refilling of the ion channels involved in cardiac action potentials. Similarly, durations like 200 ms and 300 ms do not reflect the commonly accepted measurements found in cardiology. Therefore, 250 ms is the most accurate representation of the absolute refractory period in heart muscle, highlighting its importance in maintaining a regular heart rhythm and overall cardiac health.