Guide-catheter-induced ostial coronary artery dissection is a feared complication of percutaneous coronary intervention, but thankfully the incidence is low. We describe a case of catheter-induced ostial dissection of the left internal mammary artery (LIMA) with multiple radial jump grafts during percutaneous coronary intervention of radial graft bifurcation disease via the LIMA. The dissection led to loss of flow and profound haemodynamic compromise and cardiac arrest as the LIMA supplied the majority of the myocardium in this patient. Intravascular ultrasound was not immediately available, so an Export AP thrombus aspiration catheter (Medtronic) was used over the coronary wire in place to allow the injection of contrast while simultaneously pulling back on the catheter to delineate the extent of the dissection and guide accurate drug-eluting stent placement. The report is a cautionary tale to the reader to treat the LIMA with respect and think long and hard before considering any interventional procedure that uses the LIMA as a conduit.