T Wave

The T wave represents ventricular repolarization. Normally, they are positive deflections throughout the EKG except leads aVR and V1. Although their individual duration is typically not measured (as it is a part of the QT interval), the amplitude and morphology of the T waves should be evaluated. Normally, they are somewhat asymmetric waves with an amplitude <5mm in limb leads and <10mm in the chest leads. 

As pictured above, numerous morphologies may indicate pathology. Tall, symmetric, peaked T waves are concerning for hyperkalemia. Tall, symmetric, broad T waves are usually hyperacute T waves of an early OMI. Inverted T waves may be a sign of reperfusion, active ischemia, demand ischemia, increased intracranial pressure, or from a depolarization abnormality ('secondary T wave inversions'). Flat T waves are very nonspecific findings and may be from a normal variant, ischemia, or electrolyte abnormalities. Biphasic T waves may be from ischemia, reperfusion, secondary changes, electrolyte abnormalities, or medications. 

Sometimes, additional waves called U waves are present after the T wave. It is usually a small deflection and commonly positive. U waves are incompletely understood, though usually result from severe hypokalemia or bradycardia.