Final answer:
The cardiac catherization technique used to determine the severity of mitral regurgitation is left ventriculography.
Step-by-step explanation:
The cardiac catherization technique used to determine the severity of mitral regurgitation is left ventriculography. Left ventriculography is a diagnostic procedure that involves injecting a contrast dye into the left ventricle of the heart and taking X-ray images to assess the function of the mitral valve and the severity of regurgitation.