Objective: The aim of the present study was to investigate the relationship between nightmares and acute myocardial infarction (AMI) occurring during sleep, and also to evaluate the influence of several related factors. Method: The sample comprised AMI patients who had been admitted to the coronary care unit. The patients were grouped into two categories; the asleep-AMI group consisted of 36 patients who had the onset of symptoms of AMI during sleep, and the awake-AMI group included 183 patients who had AMI while they were awake. The sleep quality and dream anxiety for the 1-month interval before AMI were assessed with Pittsburgh Sleep Quality Index (PSQI) and Van Dream Anxiety Scale (VDAS), respectively. Results: Asleep-AMI patients reported significantly poorer subjective sleep quality, significantly higher global PSQI scores, and displayed significantly higher nightmare frequency, difficulty in falling asleep after a nightmare, higher autonomic hyperactivity, dream recall frequency, daytime anxiety, psychological problems, and higher global dream anxiety scores than awake-AMI patients. Conclusion: The present study suggests that sleep anxiety and related emotions are associated with AMI during sleep. © 2011 The Academy of Psychosomatic Medicine.