Highest heart rate values (in beats per minute) before surgery and during the first 192 postoperative hours for the 663 included patients. Box and whisker plots illustrate median (line through the box), 75th percentile (top line of box), and 25th percentile (bottom line of box). There is a significant (P < 0.0001) interaction between time and groups (β-blockers reintroduced vs. β-blockers not reintroduced) after 96 h (P < 0.0001).