To assess the relationship between sustained maximal inspiratory pressure (SMIP) and maximal inspiratory pressure (MIP) and a number of physiologic and functional parameters in patients with heart failure (HF), 50 male veterans with HF had measurements of MIP and SMIP taken with the PrO2 device, which were calculated from residual volume (RV) during initial inhalation and to total lung capacity (TLC), respectively. Pulmonary function and maximal expiratory pressure (MEP) were also examined. Exercise capacity was evaluated via cardiopulmonary exercise testing (CPET) and leg strength testing; physical function was calculated with grip strength, 6-minute walk distance (6MWD), and sit-to-stand test (STS). The mean (±SD) MIP and SMIP were 66.3±24.8 cmH2O and 351.3±151.4 PTU, respectively. Both MIP and SMIP were significantly associated with many physiologic and functional measures, with the greatest correlate to MIP being MEP and the greatest correlate to SMIP being FEV1. The greatest physiologic correlate to MIP and SMIP was CPET peak tidal volume, with identical r-values (.48). Absolute and relative peak oxygen consumption (pVO2) were correlated to both MIP and SMIP, with identical r-values for absolute pVO2 (.33) and slightly higher r-values between MIP and relative pVO2 (.37 vs .34). The greatest functional correlate to MIP and SMIP was leg strength/endurance, followed by STS and 6MWD.