In some cases of congestive heart failure (CHF), localisation of pleural fluid in the pulmonary fissures with tumour like appearance on chest radiography (termed as vanishing tumour or Phantom tumour or pseudotumour) and its resolution with diuretic treatment is well documented. But localisation of fluid in the right para-mediastinal pleural space in CHF simulating a mediastinal tumour is very rare and to the best of our knowledge has not been published before in India. We report a case of a localised right-sided para-mediastinal transudative pleural effusion in an elderly woman with left ventricular failure. Anti-cardiac failure treatment including intravenous diuretic led to rapid clinical improvement and spontaneous disappearance of para-mediastinal effusion after four days. Right paramediastinal effusion re-appeared in the same area once cardiac failure returned after anti-hypertensive treatment was discontinued for about a month. Vanishing tumour associated with cardiac failure may occur anywhere in the pleural space if there is a predisposing factor favouring its localisation and recur if the underlying cause, like CHF returns.