Does your family have any history of heart disease? If not, there is nothing to worry about. I know it's easier said than done, I worry about my heart even though I have no family history of heart disease and have visited a cardiologist twice in the last couple years. Just know that if there was anything that could cause a heart attack, e.g. atheroscleorosis or icschemic muscle damage, it would have definitely been picked up by the echo and EKG.
Lathouxaris raises a good point about the fact that your extensive tests would have picked up on the possibility of an impeding heart attack as they would have shown any damage or blockage of arteries.
I do realise that you are probably thinking "but what about those heart attacks where people have normal hearts on autopsy"? (because those are the ones in newspaper articles that scare many of us)
I'm no expert but I suspect that there are different types of symptoms based on the types of heart attacks and that pain down the arms is more related to the types of heart attacks brought on by longstanding heart damage eg from atherosclerosis etc and thus would have been picked up by any tests you've had.
Yes, you do hear of people dying of heart attacks and having healthy looking hearts on autopsy but they seem to be caused by arrhythmia-type heart attacks (eg long QT syndrome) and often the symptomology is different, eg fainting and then death. Also, when younger people pass away from a suspected heart attack and the heart looks healthy, the ME often looks for other factors that might have contributed to the heart attack because sudden death from heart attack in someone under 40 is so rare.
As for my close relatives, one actually had a heart attack 2 weeks before she died and she spent time in hospital. She was then released and went to stay with another relative and then just got up to do something and collapsed and never gained consciousness. She had unusual symptoms before the first attack and didn't complain of any pain the second time. I do put things into a time context there because it is quite possible that if she had had her first heart attack 20-30 years later, she may have received different treatment as the knowledge in the 1970s isn't the same as now. So even though she was given the all clear the first time, I have no idea what treatment she received back in the day.
So, in summary, it strikes me that the "healthy heart" type of heart attacks and ones related to arrhythmia problems seem to cause sudden fainting/collapse. Whereas the ones caused by heart damage/blockage seem to be the ones that cause the pain down arms (due to the blockage finally becoming complete) and thus would be likely to have been picked up by extensive testing. I may be wrong but next time you do go to your doctor, it might be worth asking about whether different types of origins of heart attacks have different symptoms. As others have said, panic and stress can cause those pains as well.
Also, I do just want to make it clear that any comments I make above are only based on the fact that you have had extensive testing. If it had been your very first time of having those pains then I would tell you to go to your doctor. In the end, none of us are professionals and it is your doctor whom you should listen to, not us.