The risk of catheter-related sepsis and clot formation in patients with an indwelling central venous line is well recognized. However the risk of developing a large thrombus in the right atrium is less well known. Right atrial thrombus can be a life-threatening complication of long-term indwelling catheters and should be considered in the workup of these patients. A case of a 71-year-old lady who developed a large atrial thrombus due to a Hickman catheter is reported that required open heart surgery. Incidence, pathophysiology, clinical presentation, diagnosis, and treatment options are also reviewed.