The incidence of spontaneous pneumothorax has been estimated to 7.4-18.0/100,000 for men and 1.2-6.0/100,000 for women. The most common symptoms are sudden chest pain and dyspnoea. Due to chest pain many patients have an electrocardiogram (ECG) done in the acute setting. We present a case of unusual findings of electric alternans in the electrocardiogram (ECG) in a patient with a left-sided spontaneous pneumothorax. Reviewing the literature we found five former cases of pneumothoraxes with electric alternans in the ECG, all occurring in relation to left-sided pneumothorax.