No. ECGs are very reliable. They obviously can't show every possible problem with your heart however there would be tell tale signs to the doctor who would the. Refer you on for further tests if it didnt look normal.

I must have had over a dozen ECGs in the past 7 months and everyone has been normal yet I still worry. The other week a doctor actually talked me through what and the different lines and squiggles mean. He showed me what they look for and drew what an 'abnormal' ECG would look like. This have me so much reassurance and I'm so grateful to him for taking the time to explain rather than just saying yep it's normal.

Trust the doctors, they know what they are doing with this kind of thing!