Final answer:
The hallmark feature of systolic heart failure is a low ejection fraction (EF), which indicates the heart's impaired ability to contract and effectively pump blood.
Step-by-step explanation:
The hallmark feature of systolic heart failure is a low ejection fraction (EF). The ejection fraction is a measurement of the percentage of blood leaving your heart each time it contracts. In systolic heart failure, the heart's left ventricle loses its ability to contract normally, which means it can't pump blood effectively. This condition leads to pulmonary congestion because fluids get backed up in the pulmonary capillaries, causing symptoms like basilar crackles and limiting activities of daily living (ADLs). However, low EF is the primary indicator that differentiates systolic heart failure from other types of heart failure.