Pericardial effusion in oncological patients is a common finding, often caused by cancer metastasis to the pericardium, including lung, breast, melanoma, and lymphoma. Other causes include radiation therapy, infections, and primary pericardial tumors. Diagnosis is usually incidental, but cancer accounts for about one-third of cardiac tamponades. Management depends on the cause and clinical presentation. Pericardiocentesis is used for drainage when effusion causes hemodynamic impairment, and a pericardial catheter is placed for 2-5 days after fluid removal. Conservative management is advised for stable patients, though monitoring frequency is unclear. Immune checkpoint inhibitors may respond to corticosteroids, and pericardiocentesis can confirm neoplastic cells, though cytological yield is low. New pericardial effusion in non-cancer patients may suggest malignancy if there is a history of cancer, persistent course, large effusion, or unresponsive to NSAIDs. Cancer-related effusion is more common in patients with a history of cancer or recent treatment. Radiation therapy can cause effusion months to decades after treatment. Pericardial effusion from cancer treatment is often managed with corticosteroids, and in some cases, surgical intervention or catheter placement is needed. Pericardial effusion can also be caused by non-cancer factors, such as infections or heart failure. The management of pericardial effusion in oncological patients requires a multidisciplinary approach, considering both cancer and non-cancer causes. The article provides guidance on diagnosing and managing pericardial effusion in oncological patients, emphasizing the importance of considering malignancy in cases of new effusion.Pericardial effusion in oncological patients is a common finding, often caused by cancer metastasis to the pericardium, including lung, breast, melanoma, and lymphoma. Other causes include radiation therapy, infections, and primary pericardial tumors. Diagnosis is usually incidental, but cancer accounts for about one-third of cardiac tamponades. Management depends on the cause and clinical presentation. Pericardiocentesis is used for drainage when effusion causes hemodynamic impairment, and a pericardial catheter is placed for 2-5 days after fluid removal. Conservative management is advised for stable patients, though monitoring frequency is unclear. Immune checkpoint inhibitors may respond to corticosteroids, and pericardiocentesis can confirm neoplastic cells, though cytological yield is low. New pericardial effusion in non-cancer patients may suggest malignancy if there is a history of cancer, persistent course, large effusion, or unresponsive to NSAIDs. Cancer-related effusion is more common in patients with a history of cancer or recent treatment. Radiation therapy can cause effusion months to decades after treatment. Pericardial effusion from cancer treatment is often managed with corticosteroids, and in some cases, surgical intervention or catheter placement is needed. Pericardial effusion can also be caused by non-cancer factors, such as infections or heart failure. The management of pericardial effusion in oncological patients requires a multidisciplinary approach, considering both cancer and non-cancer causes. The article provides guidance on diagnosing and managing pericardial effusion in oncological patients, emphasizing the importance of considering malignancy in cases of new effusion.