Left-ventricular dysfunction is diagnosed when the heart rate performance curve (HRPC) of patients deflects upwards during incremental exercise. The aim of this study was to investigate the effect of exercise training on the upward deflection of the HRPC in patients with cardiovascular disease.This study comprised 11 patients who had cardiovascular disease and showed an upward deflection of the HRPC. The patients underwent exercise training (aerobic training, AT intensity: 30-40 minutes, 2-3 sessions/week, and 3-month follow-up). The HRPC of the patients was measured before and after exercise training. We used a method described by Pokan for evaluating the HRPC; the performance curve (PC) index ([PC1 - PC2] × [1 + PC1 × PC2]^-1) was calculated from PC1 and PC2. PC1 and PC2 refer to the heart rate response before and after the O₂ pulse deflection point, respectively. The PC index indicates the following: PC > 0.1, downward deflection; -0.1 ≤ PC ≤ 0.1, linear time course; PC < -0.1, upward deflection.The PC index significantly increased after exercise training (from -0.22 ± 0.09 to -0.14 ± 0.07; p < 0.05). In addition, the HRPC of 4 patients (37%) changed in linear time course.These results suggest that an upward deflection of the HRPC in patients with cardiovascular disease may shift to a linear time course after exercise training.