Post-infarction ventricular septal defect (VSD) is a fatal mechanical complication of myocardial infarction. Although the incidence has decreased to less than 1% after the extensive use of reperfusion strategies, post-infarction VSD still carries a high mortality risk. Management is controversial, whether to wait for surgery after a stabilisation period or to perform emergency surgery when diagnosed. We report on a case of post-infarction VSD that was detected with severe haemodynamic instability, beginning immediately after the patient's Valsalva manoeuvre on the sixth day of a non-reperfused inferior myocardial infarction. In the early period, the post-infarction VSD was repaired via a trans-aneurysmal approach.