When I was about 10 years old, I was diagnosed with an enlarged heart. As I got older, my heart eventually was normal size. I have never been able to do a lot of physical work due to tiring easily. At about 39-40 years of age, I had a stress test. The doctor told me I flunked after 5 minutes even though they kept me on the tread mill for 15 minutes. There was no blockage, but the doctor said it appeared the lower part of my heart was damaged. Now at 60 I had another stress test. During the test, my doctor asked if I had ever had a heart attack. Now the doctor has sent a letter stating the stress test scan was negative. Over the last several weeks, my heart starts beating very fast. Usually it is when I am in bed or in my recliner. Could my heart be damaged from being enlarged and now show normal on the stress test? Thank you.