What is the primary factor in determining the severity of heart failure?

Ejection fraction (EF) is a crucial measure of how well the heart is pumping blood and serves as a key indicator of heart function. In heart failure, a reduced ejection fraction, typically defined as less than 40%, signifies a significant impairment in the heart's ability to contract and effectively deliver blood to the body. This level of EF is associated with worse outcomes, increased symptoms, and a higher risk of complications.

A low ejection fraction indicates that the heart is not only struggling to meet the body's demands but also reflects the underlying pathophysiological changes occurring in the heart muscle, such as dilation and hypertrophy. Thus, it is a reliable determinant of the severity of heart failure and guides treatment decisions and prognostic assessments.

While factors like patient age, comorbidities, history of myocardial infarction, and presence of arrhythmias certainly play roles in the overall management and prognosis of heart failure, ejection fraction specifically provides direct insight into the heart's contractile function, which is foundational in understanding the severity of the condition.