Thanks for your question on Health Care Magic.
I can understand your concern.
No,
costochondritis can cause cause heart palpitations and heaviness in heart.
But no need to worry for heart diseases because your ecg is normal.
Possibility of uncontrolled
anxiety as a cause for your palpitations and heavy heart beat is more.
So better to
consult psychiatrist first. Get done counseling sessions and try to identify stressor in your life.
Start working on its solution. You may need additional anxiolytic drugs too. So avoid stress and tension, be relax and calm.
Don't worry, you will be alright.
Hope I have solved your query.
I will be happy to help you further.
Wish you good health. Thanks.