['The authors analyzed the association between outpatient β-blocker type and day-of-surgery (DOS) heart rate in ambulatory surgical patients. They further investigated whether differences in DOS heart rate between atenolol and metoprolol could be explained by once-daily versus twice-daily dosing regimens.', 'Retrospective observational study.', 'Veterans Administration hospital.', 'Ambulatory surgical patients on long-term atenolol or metoprolol.', 'None.', 'Using a propensity-score-matched cohort, DOS heart rates were compared in patients prescribed atenolol versus metoprolol. Then, once-daily and twice-daily metoprolol formulations were differentiated and DOS heart rates were compared within a general linear model. DOS heart rates in patients prescribed atenolol versus any metoprolol formulation were slower by a mean of 5.1 beats/min (66.6 v 71.7; 95% confidence interval [CI] of difference, 1.9-8.3; p = 0.002), a difference that was not observed in preoperative primary care visits. The general linear model showed that patients prescribed atenolol (typically once-daily dosing) had a mean DOS heart rate 5.6 beats/min lower compared with patients prescribed once-daily metoprolol succinate (68.9 v 74.5; 95% CI of difference, -8.6 to -2.6; p < 0.001) and 3.8 beats/min lower compared with patients prescribed twice-daily metoprolol tartrate (68.9 v 72.7; 95% CI of difference, -6.1 to -1.6; p < 0.001). DOS heart rates were similar between different formulations of metoprolol (95% CI of difference, -1.0 to +4.6; p = 0.22).'] Is atenolol associated with lower day-of-surgery heart rate compared to long- and short-acting metoprolol?