Carvalho, Vitor Oliveira, et al. “ The Relationship Between Heart Rate Reserve and Oxygen Uptake Reserve in Heart Failure Patients on Optimized and Non-Optimized Beta-Blocker Therapy ”. Clinics, vol. 63, no. 6, Jan. 2008, pp. 725-30, https://doi.org/10.1590/S1807-59322008000600003.