What does the T wave indicate on an ECG?

The T wave on an electrocardiogram (ECG) represents ventricular repolarization. This is a critical phase in the cardiac cycle when the ventricles, having already contracted and ejected blood during the preceding phase (the QRS complex), are returning to their resting state. The significance of the T wave lies in its role in ensuring that the heart is prepared for the next contraction; proper repolarization allows the cardiac muscle cells to reset their electrical state and be ready for the next action potential.

Understanding the phases of the cardiac cycle is essential; the P wave indicates atrial depolarization, which is the electrical activity associated with the atria contracting, while the QRS complex denotes ventricular depolarization (the contraction of the ventricles). Atrial repolarization occurs concurrently with the ventricles contracting, but it is usually obscured by the QRS complex and does not produce a distinct wave that is easily identifiable on the ECG. Thus, recognizing that the T wave signifies the time when the ventricles are resetting and getting ready for the next heartbeat is crucial in interpreting ECGs correctly.