50-55% indeed is low normal. There are some things you might consider to ease your mind:
-If measured with a ultrasound device, it could well be that it actually is 55-60%, as echos are not the most reliable way to measure EF.
-Perhaps you were born with it and 50-55% is normal for you
-If it has become lower than it used to be, it can go up again. Exercise can help strengthen your heart and improve how well it pumps blood to the rest of the body. All it takes is 30 minutes a day of activity, even if that activity is walking.
Mild regurgitation is nothing to worry about. Many people have some leakage in one or more of their heart valves and never know about or notice it until an echo is made.
As it is (mild), it does not harm your heart and there is a big chance that the regurgitation will never get worse.
So, with the info you provide I have to agree with your cardiologist. You have nothing to worry about.
Sorry, I meant *EF not EJ!