The U wave on an ECG is described as:

• A. An abnormal downward deflection preceding the QRS complex.
• B. The normal, small upward curve that occasionally follows a complete ECG cycle after the PQRST; has unknown indication.
• C. A wave that represents atrial contraction.
• D. A large positive deflection after the T wave.

Answer: (B)

The U wave is a small, positive deflection that can appear after the T wave, following the complete QRS-PQRST cycle. It’s a normal finding when it’s small, but its exact significance isn’t clearly established. This is why the description of a normal, small upward curve that occasionally follows the full cycle after the PQRST—with an unknown indication—fits best. The other descriptions point to different features: a downward deflection before the QRS is the Q wave, the wave that represents atrial contraction is the P wave, and a large post‑T deflection isn’t typical of a U wave.