Ischemic Cardiomyopathy: This is the most common cause of a severely reduced ejection fraction. It occurs when the heart muscle is damaged due to a lack of blood flow, often as a result of a heart attack. The damage leads to a significant decrease in the heart's ability to pump blood efficiently.

Dilated Cardiomyopathy: A condition where the heart becomes enlarged and cannot pump blood effectively. It can be caused by various factors, including genetics, infections, and alcohol abuse.
Heart Failure with Reduced Ejection Fraction (HFrEF): A condition where the heart's ability to pump blood is severely impaired, leading to symptoms such as shortness of breath, fatigue, and swelling.
Valvular Heart Disease: Conditions such as mitral regurgitation or aortic stenosis can lead to a reduced ejection fraction if left untreated or if treatment is delayed.

Cardiac Amyloidosis: A rare condition where abnormal proteins accumulate in the heart, leading to stiffness and reduced function. It can be fatal if not diagnosed and treated promptly.
Hemochromatosis: A genetic disorder that leads to iron overload, which can cause heart failure and a reduced ejection fraction if not treated.
Pulmonary Embolism: A blockage in one of the arteries in the lungs, which can lead to acute right heart failure and a reduced ejection fraction.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): A rare genetic disorder that affects the heart muscle, leading to abnormal heart rhythms and a reduced ejection fraction.
Left Ventricular Non-Compaction: A rare congenital heart condition where the heart muscle does not develop properly, leading to a reduced ejection fraction.
Giant Cell Myocarditis: A rare and potentially fatal inflammatory condition that affects the heart muscle, leading to a reduced ejection fraction.