Hypercalcemia is commonly encountered in the clinical setting. Although primary hyperparathyroidism resulting from a single parathyroid adenoma is the most common cause, in patients who undergo total thyroidectomy, especially when there is no history of radiation exposure nor parathyroid autotransplantation, it becomes an even more unexpected diagnosis. Because the majority of patients are asymptomatic, the diagnosis often is made incidentally. However, with long-standing disease, as parathyroid hormone and blood calcium levels rise, symptoms become more noticeable, and its clinical manifestations can affect nearly every organ system in the body. We present the case of a 79-year-old woman with a history of surgical hypothyroidism secondary to total thyroidectomy, hypertension and chronic kidney disease, who was admitted to the Emergency Department after an episode of syncope. She mentioned abdominal pain and vomiting in the previous week and paresthesia of both hands and feet over the last months. The initial testing identified a first-degree auriculoventricular block, a worsened renal function and severe hypercalcemia caused by primary hyperparathyroidism. The mainstay of treatment was aggressive fluid therapy, intravenous bisphosphonate and calcimimetic. Definitive treatment was achieved by the surgical removal of a mass located in the left thyroidectomy bed, compatible with a parathyroid adenoma. No further therapy was needed, as calcium levels gradually returned to normal.