The aim of this study was to examine the quality of life and to report on the utility and QALY measures in patients before and after coronary artery bypass grafting (CABG); to investigate whether the SF-12 is comparable with the SF-36 for measuring health-related quality of life of patients with CABG; and to determine the impact of individual predictors on poor quality of life assessment after rehabilitation. This prospective study was conducted between January 2017 and December 2018 at the University Hospital Center Osijek, at three time points: pre-operation, 1 month after surgery, and after rehabilitation. The study was conducted with the SF-36 and SF-12 health questionnaires on 47 participants. After rehabilitation, there was a significant improvement in all domains of quality of life. The highest score was given to the change in pain (BP); mean scores were 63.8 (95% CI 56.9 to 70.6) (p = 0.001). The lowest grade (the lowest quality) after rehabilitation was in the domain of limitations due to physical difficulties (RP); arithmetic mean was 48.5 (95% CI 41 to 55.9) (p < 0.001). Quality-adjusted life-year was 0.41 (95% CI 0.38–0.44) after the CABG. The results of this study show that patients with coronary heart disease have poor quality of life before surgery. One month after the surgery, the quality of life improved, but was still inadequate. One year after surgery, satisfactory results were obtained in almost all subscales. The SF-36, SF-12, and its components, can be used effectively in patients with CABG. Age, gender, lifestyle, and risk factors in our sample of participants are not predictors of poor quality of life assessment after rehabilitation.