Which of the following conditions is characterized by heart failure with an ejection fraction of ≤ 40%?

Systolic heart failure is characterized by a reduction in the heart's ability to pump effectively during the contraction phase of the cardiac cycle, leading to a lower ejection fraction. An ejection fraction of ≤ 40% indicates that the heart is not pumping enough blood to meet the body's needs, which is a hallmark of systolic dysfunction. This contrasts with diastolic heart failure, where the ejection fraction is often preserved (> 40%), but the heart has difficulty filling properly due to stiffness or reduced relaxation.

Conditions such as aortic stenosis and mitral stenosis affect the heart valves and can lead to heart failure but do not inherently determine the ejection fraction in the same way as systolic heart failure. Aortic stenosis can lead to a decreased ejection fraction over time due to pressure overload on the left ventricle, but it is not synonymous with systolic heart failure. Mitral stenosis primarily affects filling but generally retains a better ejection fraction, as it is more related to diastolic dysfunction. Thus, the characteristic of an ejection fraction of ≤ 40% is definitive for systolic heart failure.