Greetings : A number of possibilities may account for the pain Ranging from cardiac to non cardiac there are many possibilities! since history suggest that xray and ECG are normal the cause would be something as simple Stress or Gastrointestinal conditions like heartburn, Hiatal hernia, gallbladder or pancreatic conditions! Some of the other Rare cause include Tietze s Syndrome Pinched nerves Sore muscles Fibromyalgia Precordial catch syndrome only after through examination and history the cause can be found out and treated!