A 54 years old gentleman was admitted to cardiology ward from echocardiography department in view of findings on the scan. He was referred to cardiology clinic on outpatient basis 3 months earlier by his GP for his shortness of breath, ankle swelling and a murmur heard on auscultation by his GP. His transthoracic echocardiography was being conducted prior to attendance at cardiology clinic. The result showed a large global pericardial effusion, max 4.9 cm in size. There was severe aortic regurgitation as well. He underwent thyroid function test as part of screening to find out cause for pericardial effusion and his TSH was 186 mU/l along with T4 of 5.4 pmol/l. His anti-TPO was elevated at 289 U/ml. At this point an endocrinology opinion was sought. On further questioning the patient mentioned that he was feeling tired, lethargic, cold and constipated for the last 3 months, along with noticing the shortness of breath and swelling to his ankles. He also noticed that his skin was feeling dry and had noticed some hair loss. He was also feeling low in mood. There was no past medical history of note. On examination he had facial plethora and loss of eyelashes. He also had slow relaxing ankle reflexes. A diagnosis of primary hypothyroidism was made. Subsequently he was started on low dose levothyroxine and the dose was gradually titrated up. A discussion was held in cardiology MDT meeting and it was decided to manage his pericardial effusion conservatively. He stayed in hospital for 10 days and started to feel better after initiation of levothyroxine. This case illustrates that hypothyroidism should be considered in the differential diagnosis of patients presenting with unexplained pericardial effusion.