An EF of 80% may be a normal condition at a specific time interval altough it is outside the normal EF 55 to 75%; EF represents the percentage of blood pumped into circulation with each heartbeat.
The EF represents a mechanism that helps maintain a balance between the left and right side of the heart. If the left side is out of balance, the left ventricle will dilate to increase stroke volume and stronger contractility to compensate. Not unlike a compensatory increase of the heart rate.
A problem develops when there is sustained overcompensation. The dilation stretches the heart's capacity to a point where contractility is reduced, and this conditrion will eventually lead to heart failure (EF below 29%). The imbalance of more blood rec'd to the LV than pumped out into circulation causes the blood to back up into the lungs (congested heart failure).
Ejection fraction refers to the percentage of blood that is pumped out of the heart ventricle with each heartbeat. A normal ejection fraction is 55 to 75 percent. An EF of less than 40 percent indicates that the heart muscle has been damaged and is not functioning properly
An LVEF over 75% is considered too high, or medically-termed as being a hyperdynamic or a hypercontractile left ventricle (LV), that is, the heart is pumping forcefully, an excessive amount of blood is being pumped out.
According to various medical literature, there a few specific clinically-recognized causes of a hyperdynamic/hypercontractile left ventricle, which includes aortic valve regurgitation (leakage), sometimes the mitral valve, hypermetabolic states (thyrotoxicosis, anemia), some congenital heart defects (e.g., large patent ductus arteriosus, and ventricular septal defect), and hypertrophic cardiomyopathy (HCM). The condition may/can also be deemed as idiopathic (no known cause).
You may want to ask this on the expert forum. I hope this helps.
Jon