OBJECTIVE: Stress has been cited as a causal factor in heart disease. The objective of this study was to examine the effects of an 8-week mindfulness-based stress-reduction program on the resting levels of stress hormones, physical functioning, and submaximal exercise responses in women with heart disease. SUBJECTS: Random selection with the numbers 1 and 2 were used to assign 18 women (60 +/-6.3 years old) with documented histories of heart disease to a treatment group (n = 9) or a control group (n = 9). Speilberger's state anxiety scores for the treatment (M = 37.88; standard deviation (SD) = 10.91) and control group (M = 43.22; SD = 12.26) were not significantly different prior to the start of the study. However, their scores fell in the upper percentile rank for normal adults in their age category. INTERVENTION: The intervention was provided one night each week for 2 hours over a period of 8 weeks. The intervention included didactic, inductive, and experiential modes of learning regarding stress responses and mindfulness skill-development training. DESIGN: Pre-post test hormonal measurements and physical function were analyzed using a 2 (group) by 2 (time) analysis of variance (ANOVA) with repeated measures following the 8-week program. Submaximal exercise responses were also compared between the treatment group and the control group following the 8-week program. A 2 (group) by 3 (time) ANOVA with repeated measures was used to analyze the data. SETTINGS/LOCATION: Weekly meetings were held on a university medical school campus. Submaximal exercise responses were recorded while participants cycled on a stationary bike in an applied physiology laboratory following the 8-week program. RESULTS: There were no significant main effects or interaction for the resting levels of stress hormones or physical functioning. There were no significant interactions for the submaximal exercise responses, however, there were significant main effects between groups for ventilation [F(2,32) = 7.65, p < .01, f = 0.8], and between group [F(1,16) = 8.84, p < .01, f = 0.8] and time [F(2,32) = 10.42, p < .01, f = 0.9], for breathing frequency. CONCLUSION: While the 8-week stress reduction program for women with heart disease did not show significant interactions between groups for resting levels of stress hormones, physical functioning, or submaximal exercise responses, there was a significant difference in breathing patterns between the 2 groups during exercise following the mindfulness-based stress-reduction program. There was also a trend for change in the intervention group in the resting levels of cortisol and physical function scores that was not seen in the control group. Future studies could use the effect size generated from this pilot study to calculate the number of subjects needed for adequate power to detect significant differences between groups.