INTRODUCTION Slow breathing training (SBT) has been proposed as a new nonpharmacologic treatment in patients with chronic heart failure (CHF). OBJECTIVES The aim of this study was to assess the effects of SBT on exercise capacity, hemodynamic parameters, and sleep respiratory patterns in a relatively large sample of CHF patients. PATIENTS AND METHODS A crossover open study was conducted. Patients completed, in a random order, 10- to 12‑week SBT, with 2 15‑minute sessions of device‑guided SBT each day, reaching 6 breaths/ min, and a 10- to 12‑week follow‑up under standard care. Clinical data collection, polysomnography, echocardiography, 6‑minute walk test (6MWT), and laboratory tests were performed. RESULTS A total of 96 patients (74 men, 22 women) in New York Heart Association classes I-III, with an average age of 65 years and an ejection fraction (EF) of 31%, completed the study. Home‑based SBT was safe. After training, EF and 6MWT distance improved (EF: 31.3% ±7.3% vs 32.3% ±7.7%; P = 0.030; 6MWT: 449.9 ±122.7 m vs 468.3 ±121.9 m; P <0.001), and the apnea-hypopnea index decreased (5.6 [interquartile range (IQR), 2.1; 12.8] vs. 5.4 [IQR, 2.0; 10.8]; P = 0.043). CONCLUSIONS SBT improved physical capacity and systolic heart function; it also diminished sleep disturbances. The results support the benefits of SBT as a novel component of cardiorespiratory rehabilitation programs in patients with CHF.