A newly developed critical pathway has been applied to emergency medical care of patients with acute myocardial infarction (AMI) in the emergency department. The arrival-in-cath-lab interval (ACI) was selected as a clinical indicator of quality assurance, according to American Heart Association and American College of Cardiology guidelines. This report describes the first experience of applying the critical pathway to patients with AMI in an emergency department in Japan. The ACI of 35 AMI patients who underwent primary percutaneous transluminal coronary angioplasty during a 24-month period following application of the pathway were compared with those of 50 AMI patients during the 48 months before application of the pathway. The median ACI value was significantly reduced from 65.5 min to 50.0 min. Also, the proportion of patients with acceptably short ACI (<60 min) significantly improved from 42.0% to 68.6%.