Gastroesophageal Reflux Disease (GERD): This is often the most common cause of chest pain with a normal ECG. The pain can mimic cardiac ischemia but is usually related to eating or lying down and can be accompanied by regurgitation or dysphagia.

Musculoskeletal Pain: Chest wall pain or costochondritis can cause significant discomfort that may be mistaken for cardiac pain. This type of pain is usually reproducible with palpation or movement.
Anxiety or Panic Disorder: These conditions can cause chest pain or discomfort that is not related to cardiac disease. Patients may also exhibit other symptoms such as shortness of breath, palpitations, or fear of dying.
Pulmonary Embolism (with a normal ECG): While many pulmonary embolisms present with abnormal ECG findings, some may have a normal ECG. The presence of risk factors (e.g., recent surgery, immobilization, cancer) and symptoms like sudden onset dyspnea or tachypnea should raise suspicion.
Pericarditis: Although pericarditis often presents with ECG changes, early stages or mild cases might have a normal ECG. The pain is typically sharp, pleuritic, and improves with sitting up and leaning forward.

Aortic Dissection: This is a life-threatening condition that requires immediate diagnosis and treatment. The pain is often severe, tearing, and radiates to the back. A high index of suspicion is needed, especially in patients with risk factors like hypertension or aortic aneurysm.
Pulmonary Embolism (even with a normal ECG): As mentioned, while some ECGs may be normal, the risk of missing this diagnosis is too high to not consider it, especially with symptoms like sudden dyspnea or chest pain.
Myocardial Infarction with Normal ECG: Early in the course of a myocardial infarction, the ECG may be normal. This is particularly true for non-ST elevation myocardial infarctions (NSTEMI). Clinical suspicion based on symptoms and risk factors is crucial.

Esophageal Spasm or Rupture: These conditions can cause severe chest pain and are less common than other diagnoses. Esophageal rupture is a medical emergency.
Pneumothorax: While often associated with lung disease, a spontaneous pneumothorax can occur in healthy individuals and cause sudden onset chest pain and shortness of breath.
Mediastinitis: Inflammation of the mediastinum can cause chest pain and is often associated with infection or trauma. It is a rare but serious condition.