Phantom tumour, vanishing tumour, and pseudotumour of the lung are terms used to describe the tumour appearance on a chest radiograph of a decompensated heart failure patient, which typically disappears after appropriate treatment of their underlying condition. It is a loculated pleural effusion in the fissures that gives rise to the tumour appearance on the chest radiograph of a patient with heart failure. Its existence might mislead the diagnosis, resulting in unnecessary invasive diagnostic investigations done on the patient. We present a case of a 64 year-old male with multiple co-morbidities presenting with dyspnea, loss of weight, and loss of appetite. A chest radiograph showed homogenous opacity over the right lower zone with cardiomegaly, raising the suspicion of a lung mass apart from heart failure. It disappeared after appropriate diuretic treatment. The computed tomography (CT) thorax, which was planned by the primary team, subsequently showed no lung mass. Hence, a high index of suspicion of phantom tumour is important when a lung mass is noted on a chest radiograph of a patient clinically presented with heart failure. This is because exposure to ionising radiation from CT is completely avoidable with just appropriate treatment of fluid overload. However, CT is still the best modality for assisting physicians in a doubtful case.