We present the case of a patient who underwent an acute ST-elevation myocardial infarction of the inferior wall and transitory total heart block in the first hours of his clinical presentation. There was no haemodynamic instability before the thrombolytic therapy was performed 8 h after the onset of pain. There was no block recurrence. The current case shows a possible complication during the thrombolytic therapy and the urge for a quick decision by the emergency physician. Pacemaker implantation should be considered in the event of the patient's haemodynamic worsening once the success of the therapy is a reflex of the arrhythmia reversion most of the times.