As per your description, you have undergone various consultations and procedures to rule out Heart problems.Have you consulted a Cardiologist? What is his diagnosis? Has he ruled out heart disorders?
If the answer is Yes .. No cardiac disorders, Then you need the treatment from a mental health professional.
There are drugs to relax you from your problems.In addition, Psychological interventions will give you additional benefits.
Avoid Coffee and the drinks where there is increased amount of caffeine in it.
Life style changes are also required.
Next Steps
Detailed hit and evaluation are also needed as in other psychological disorders to come to a diagnosis and management.