Perforation of the heart is a rare, but life-threatening complication of chest tube thoracostomy. We report the very unusual case where right-sided insertion of a Matthys catheter (6 F) due to pleural effusion resulted in a left atrium perforation. Heart injury was immediately considered as a continuous flow of bright red blood emerging through the chest drain. Diagnosis was confirmed by computertomography also revealing a massive cardiomegaly due to pre-existing mitral valve regurgitation. In two consecutive thoracotomies, first the Mathys drain was removed and the heart defect closed and then the mitral valve was replaced by a bio prosthesis. The extent of the cardiomegaly and the position of the left atrium were not detected pre-operatively by chest X-ray or ultrasonic device. Despite a nosocomial pneumonia, the patient fully recovered. This case shows that extreme caution is necessary when inserting chest tubes in patients where thorax imaging by X-ray or ultrasonic device does not provide a clear anatomical site. In order to minimise complications, a blunt puncturing procedure or Seldinger technique should be used and assisted by a Doppler ultrasonic device. Also early imaging by CT and Doppler ultrasonic technique should be attempted. This may reduce incidence of severe complications as in this case.