A 19 year old pregnant woman presented to the coronary care unit with an acute anterior myocardial infarction. She was treated with primary percutaneous transluminal coronary angioplasty of the proximal left anterior descending coronary artery. Ultrasound examination showed patent foramen ovale (PFO) and atrial septal aneurysm. The patient was a heterozygote carrier of factor V Leiden. Despite the lack of a clear clue, it was considered that the pathophysiological cause of this infarction was a paradoxical embolus in the left coronary artery. Pregnancy and factor V Leiden carriership are associated with increased risk of venous thromboembolism and the association between PFO and atrial septal aneurysm is a strong risk factor for systemic embolisation.