Introduction: Exercise oscillatory ventilation (EOV) is considered an important variable for predicting poor prognosis. However, there are no studies evaluating EOV in patients with coexisting COPD and heart failure (HF). Aims: I) To evaluate the presence of EOV during cardiopulmonary exercise testing (CPET) compared to no EOV (N-EOV) in patients with coexisting HF-COPD; and II) to identify the impact of EOV on the mortality during follow-up for 35 months. Methods and results: 50 stable HF-COPD patients underwent CPET and were followed for 35 months. We identified 37 (74%) patients with N-EOV and 13 (26%) patients with EOV during exercise. Patients with EOV had worse cardiac function (LVEF: 30±6% vs. N-EOV 40±9%, p=0.007), worse pulmonary function (FEV1: 1.04±0.7 L vs. N-EOV 1.88±0.7 L, p=0.007), a higher mortality rate [7 (54%) vs. N-EOV 8 (27%), p=0.02], higher  minute ventilation/carbon dioxide production (V?E/V?CO2) slope (42±7 vs. N-EOV 36±8, p=0.04), reduced ventilation peak (L/min) (26.2±16.7 vs. N-EOV 40.3±16.4, p=0.01) and oxygen uptake peak V?O2 peak (mlO2.kg-1.min-1) (11.0±4.0 vs. N-EOV 13.5±3.4 ml?kg-1?min-1, p=0.04) when compared to patients with N-EOV. When applying Kaplan-Meier analysis, we found that patients with EOV had a higher risk of mortality during follow-up (long-rank p=0.001) than patients with N-EOV. Conclusion: The presence of EOV is associated with greater severity of coexisting HFrEF and COPD and a poorer prognosis. Assessment of EOV in patients with coexisting HF-COPD, as a gauge for both clinical status and prognosis may therefore be warranted. FAPESP: 2015/26501-1 and 2018/03233-0, CAPES and CNPq.