Final answer:
Early deceleration on an ECG shows a decrease in heart rate during the contraction phase of the heart cycle.
Step-by-step explanation:
The tracing of early deceleration on an ECG shows a characteristic decrease in heart rate during the contraction phase of the heart cycle. It is associated with the onset of an action potential in the vagus nerve, which slows down the heart rate. This can be seen as a gradual downward slope on the ECG tracing.