What would cause an enlarged mitral valve with regurgitation over 4 years?

[aprilsxtn]

I had a heart attack 4 years ago when I was 31 years old.  It was a blood clot which was completely gone when the heart cath was performed and there was no damage.  A month later I was admitted for panic attack from palpitations (pvc’s) and an echo was done which came back normal.  Lately I have been having sharp constant chest pain in two different spots, 2 occurrences of pain over left breast and on the underarm side of breast, and two occurrences of localized clenching pain in middle of left chest.  Each time it lasts at least 30 minutes except for the last time it lasted for about 4 hours.  I was admitted to hospital and an echo showed that I now have an enlarged mitral valve with regurgitation.  A few days later I woke up with palpitations that lasted for about 30 minutes.  Since then my blood pressure and heart rate have been completely normal but lower than my readings over the last two years.  Any idea what can cause my mitral valve to enlarge over a period of 4 years? And why has my heart rate and blood pressure suddenly dropped to borderline low readings when they have always been borderline high?  Note that heart disease runs in my family very bad. I have two sisters that both had heart problems from young ages.  Thanks and sorry for the long post!