BACKGROUND Pericardial cyst is a rare benign mass of the mediastinum. More than two-thirds of pericardial cysts are located in the right cardiophrenic angle and less than one-third in the left cardiophrenic angle. Most cases are asymptomatic and discovered incidentally during to thoracic imaging such as chest X-ray, CT scans, and transthoracic echocardiograms. When pericardial cysts present with symptoms, they are often persistent and non-specific and include chest pain, dyspnea, and persistent cough. The optimal management of pericardial cysts is unclear, and no large studies regarding safety, efficacy, and long-term follow-up exist. Management strategies include cyst resection with sternotomy, thoracotomy or video-assisted thoracic surgery, cyst aspiration, and sclerosis after aspiration. The optimal mode of follow-up for asymptomatic cases is also unclear. Here, we present a case of a large pericardial cyst in the left cardiophrenic angle in a middle-aged Danish woman with persistent and unresolved dyspnea and chest pain. CASE REPORT A 57-year-old woman was referred for transthoracic echocardiography because of year-long cough and left-sided chest pain, which were exacerbated in the supine position. The echocardiography revealed a large cyst-like structure over the left ventricle. A cardiac CT scan and MRI scan were performed, confirming the presence of a large pericardial cyst with no communication with the pericardium. The cyst was surgically removed via thoracotomy. CONCLUSIONS Pericardial cysts should be considered as a rare differential diagnosis, giving rise to common cardio-pulmonary symptoms such as chest pain, dyspnea, and cough.