Which condition indicates a low left ventricular ejection fraction (LVEF)?

A low left ventricular ejection fraction (LVEF) is primarily associated with conditions that impair the heart's ability to effectively pump blood. Cardiomyopathy is one such condition that can lead to a reduced LVEF due to structural and functional changes in the heart muscle. In cardiomyopathy, the heart muscle can become weakened, enlarged, or stiff, impacting its contractile function and ultimately resulting in a diminished ejection fraction.

The other options do not typically lead to a low LVEF in the same direct manner. Pulmonary arterial hypertension can lead to right ventricular dysfunction over time, but it does not inherently cause a low LVEF as it primarily affects the right side of the heart. Uncomplicated Fontan circulation is a palliative surgical procedure for managing single ventricle physiology and often maintains an adequate LVEF. Turner syndrome itself is associated with various cardiac anomalies, but not all individuals will have reduced ejection fractions, particularly in the absence of congenital heart defects. Therefore, among the provided choices, cardiomyopathy is distinctly recognized as a significant contributor to a low LVEF.