Complete heart block and cardiac tamponade secondary to Merkel cell carcinoma cardiac metastases

This is a unique case of Merkel cell carcinoma, a rare neuroendocrine tumor, metastasizing to the heart and inducing a progression of cardiac complications such as new-onset atrial fibrillation, malignant pericardial effusion with tamponade physiology, first-degree heart block, and complete heart block. Metastases to the heart are relatively rare but should be Suspected if a patient with a known neoplasm presents with new cardiac manifestations. This is the first case report of cardiac metastases from Merkel cell carcinoma causing cardiac tamponade or complete heart block. This case highlights the clinical decision-making involved in managing cardiac tamponade and complete heart block in the setting of metastatic disease to the heart.