Originally Posted by mrsD

Small people have smaller hearts.

The quote you give means that:

There is a membrane around the heart called the pericardial membrane. If fluid builds up or air in that space it constricts the heart and prevents it from pumping properly. This can kill you if not fixed.

I doubt this is the woman's problem, unless she is suddenly very ill -- the heart thing in the quote is an acute situation, not a daily occurance.

If your friend was normal before and NOW has a smaller heart, that requires a doctor ASAP.

People with language issues, or from other countries, often use simple vernacular to explain things...so it might appear to be "small" but in fact the medical term might be "not enlarged".
She would use English simply and say "small".