We present a case which highlights the diagnostic difficulties between a Stanford type A aortic dissection (AD) and a pulmonary embolism (PE) and the impact it has on subsequent management. A 75-year-old man presenting with chest pain, shortness of breath and dizziness was initially suspected of having a PE and started on low-molecular-weight-heparin (LMWH). The patient was correctly diagnosed afterwards with CT of the chest to have an aortic dissection. The detrimental use of LMWH may have caused a propagation of the dissection and delayed surgical intervention of an acutely life-threatening condition. When the diagnosis is unclear, the early use of CT can help differentiate AD from PE. This in-turn can guide the management as well as the use of LMWH, which should be avoided until the correct diagnosis is confirmed.