It should be noted that the cardiovascular impairment of pectus excavatum can also be manifested during submaximal, low intensity (ie, subthreshold) exercise workouts. Malek et al45 and Malek and Fonkalsrud44 examined the time constant for oxygen uptake kinetics (τV̇o2) during submaximal workouts in pectus excavatum patients prior to and following surgical repair. Briefly, oxygen uptake kinetics is the rate at which oxygen uptake increases in response to an exercise stimulus.,51 Typically, the on-τV̇o2 (on-transient) and off-τV̇o2 (off-transient) value in young, healthy individuals is 35 s (SD, 5 s) for workouts conducted below the ventilatory threshold. However, this value can either decrease (ie, faster kinetics) with endurance training or increase (ie, slower kinetics) as a result of cardiovascular impairment. For example, Phillips et al,57 reported that the mean on-τV̇o2 and off-τV̇o2 during submaximal exercise decreased significantly from 38.1 s (SD, 2.6 s) and 38.0 s (SD, 1.0 s), respectively, to 28.3 s (SD, 1.0 s) and 30.6 s (SD, 0.9 s), respectively, after only 30 days of endurance training. Malek et al,45 examined 21 physically active pectus excavatum patients (mean severity index, 5.1; SD, 1.2) and reported mean values for on-τV̇o2 (37.4 s; SD, 10.1 s) and off-τV̇o2 (41.6 s; SD, 13.1 s) that were substantially longer than the expected values for aerobically trained individuals. Interestingly enough, however, Malek and Fonkalsrud,44 found that the on-τV̇o2 (preoperatively, 46.8 s; postoperatively, 33.6 s) and off-τV̇o2 (preoperatively, 46.5; postoperatively, 30.3 s) dramatically improved following surgical repair of pectus excavatum in a 30-year-old man (severity index, 3.7). These findings, along with the results of the present investigation, further indicate that pectus excavatum results in clinically significant cardiovascular impairment.