Spontaneous pneumothorax is an emergency that can present with variable signs and symptoms. Diagnosis of pneumothorax can be difficult, particularly in patients who present with unusual clinical findings. The electrocardiographic changes that develop with left pneumothorax are not widely known and can mimic acute myocardial ischemia. Our patient was admitted to the Cardiovascular Intensive Care Unit because of characteristic changes on the electrocardiogram. An admission chest film revealed left tension pneumothorax.