Staying in an intensive care unit (ICU) is very stressful for patients after heart surgery. Although it is a general belief that support from doctors is important to reduce patients' tension, no quantitative data are available. We investigated the stress-reducing effects of a tape-recorded message from the physician which provided information regarding the surgery and emotional support for heart surgery patients postoperatively in the ICU. Sixty patients who underwent cardiac surgery were randomly allocated to two equal groups. The patients in the experimental group listened to a tape-recorded message from their attending surgeon soon after they recovered from anesthesia, while the control group rested during the study period. The effectiveness of the tape-recorded support program was evaluated by the influence on heart rate, blood pressure, and finger skin temperature, as well as the degree of subjective pain, tension, anxiety, depression, and anger. The pain and tension levels of the patients were measured using a visual analogue scale, while the severity of anxiety, depression, and anger was evaluated using the Brief Symptom Rating Scale. Patients' evaluation of the usefulness of the program was also assessed. After listening to the physician's recorded message, the mean increase in the skin finger temperature in the experimental group was higher than in the control group (0.44 degree C vs 0.25 degree C, p = 0.0513). The experimental group had significant decreases in their mean scores of pain (-1.11 vs 0.36, p = 0.0043), tension (-2.26 vs -0.25, p = 0.0001), anxiety (-1.3 vs -0.57, p = 0.0473), and depression (-2.24 vs -0.37, p = 0.0253). The patients showed a high need for this support program (mean need score 8.4). These findings show that a physician's tape-recorded message providing information and emotional support can reduce stress in heart surgery patients in the ICU postoperatively.