How long does it typically take for the heart muscle to relax following contraction as shown in the ECG?

The typical time it takes for the heart muscle to relax following contraction, as depicted in the electrocardiogram (ECG), is approximately 0.2 seconds. This time frame corresponds to the repolarization phase of the cardiac cycle, specifically during the T wave on the ECG.

During the T wave, the ventricular muscle fibers are repolarizing, which allows them to relax after the previous depolarization and contraction (represented by the QRS complex). This phase is crucial for allowing the heart to fill with blood again before the next contraction cycle begins. The duration of 0.2 seconds aligns with the physiological processes that occur in the heart's rhythm under normal conditions and reflects the efficient timing needed for proper cardiac function.

Other options, which suggest longer durations, do not accurately reflect the current understanding of the heart's electrical activity, as they fall outside the typical timeframe established by physiological studies.