What is very rare, small foci of dense interstitial fibrosis on the heart?

Small scars: It indicates some prior damage to the heart muscle, e,g, rheumatic fever, vasculitis, viral infection and in older people atherosclerotic disease of the coronary arteries.

It sounds like...: .. you are quoting an imaging report. These words essentially mean "scar." The most common cause of myocardial/heart scar is occlusion of a blood vessel supplying that part of the heart..a heart attack. Ongoing ischemia (lack of blood supply) of heart muscle, heart enlargement or dilation and perhaps hypertension are associated with fibrosis, too. Your cardiologist will explain and advise.