BACKGROUND: Acute myocardial infarction places additional demands on an already compromised myocardium. Relaxing music can induce a relaxation response, thereby reversing the deleterious effects of the stress response. OBJECTIVES: To compare the effects of relaxing music; quiet, uninterrupted rest; and "treatment as usual" on anxiety levels and physiological indicators of cardiac autonomic function. METHODS: A 3-group repeated measures experimental design was used. Forty-five patients, 15 per group, with acute myocardial infarction were assigned randomly to 20 minutes of (1) music in a quiet, restful environment (experimental group); (2) quiet, restful environment without music (attention); or (3) treatment as usual (control). Anxiety levels and physiological indicators were measured. RESULTS: Immediately after the intervention, reductions in heart rate, respiratory rate, and myocardial oxygen demand were significantly greater in the experimental group than in the control group. The reductions in heart rate and respiratory rate remained significantly greater 1 hour later. Changes in heart rate, respiratory rate, and myocardial oxygen demand in the attention group did not differ significantly from changes in the other 2 groups. The 3 groups did not differ with respect to systolic blood pressure. Increases in high-frequency heart rate variability were significantly greater in the experimental and attention groups than in the control group immediately after the intervention. State anxiety was reduced in the experimental group only; the reduction was significant immediately and 1 hour after the intervention. CONCLUSIONS: Patients recovering from acute myocardial infarction may benefit from music therapy in a quiet, restful environment.