Final answer:
An inverted U wave on an ECG indicates ventricular tachycardia, a rapid heart rhythm originating from the ventricles.
Step-by-step explanation:
An inverted U wave on an electrocardiogram (ECG) typically indicates an abnormality known as ventricular tachycardia. Ventricular tachycardia is a rapid heart rhythm originating from the ventricles, the lower chambers of the heart. During ventricular tachycardia, the QRS complex, which represents the depolarization of the ventricles, appears abnormal and may have an inverted or wide shape. This abnormality can be detected on an ECG and is typically associated with an increased risk of serious complications.