That sounds like a pericardial fat pad, which is a small lump of fatty tissue on the outside of the heart. Cardiologists generally consider it of little or no significance. It does not affect your heart function directly. We don't know, and usually don't care, if it will go away by itself.

However, a recent study shows some association with future coronary heart disease. It may be a reflection of increased overall body fat. A few researchers speculate that it may even produce harmful chemicals. None of these have been proven.

And if these theories later prove to be true, then this fat pad would be like a warning light for people to diligently reduce their coronary risk factors, such as high blood pressure, high cholesterol,  diabetes, smoking, obesity, etc. That's actually a good idea, any way, for anybody, fat pad or no.