In this study effects of a brief mindfulness-based stress reduction intervention were examined in cardiac patients who had a percutaneous coronary intervention (PCI). One-hundred-and-fourteen patients (mean age 55 ± 7 years, 18 % women) were randomly assigned to a 4-session mindfulness group intervention or a minimal mindfulness self-help control group that received a booklet containing identical information. Compared to self-help, the group intervention showed larger increases in psychological and social quality of life (p < .05, partial η(2) = .04 and .05, respectively). For symptoms of anxiety and depression, and for perceived stress, this effect was evident only in patients younger than 60 years (p < .01, partial η(2) = .10 and .15, respectively). These effects were partially or fully mediated by increase in mindfulness. The brief group mindfulness intervention seems beneficial for cardiac PCI patients regarding general psychosocial quality of life, although for specific psychological symptoms, this intervention can be recommended only for nonelderly patients.