Abstract Aims Testosterone deficiency (TD) is associated with increased morbidity and mortality in heart failure with reduced ejection fraction (HFrEF). However, data in women are scanty. The aim of this study was to investigate the prognostic impact of TD on women with HFrEF. Methods Among 480 patients prospectively enrolled in the T.O.S.CA. (Terapia Ormonale Scompenso CArdiaco) registry, a prospective, multicentre, nationwide, observational study, 94 women were included in the current analysis. The TD was defined as serum testosterone levels lower than 25 ng/dl. Data regarding clinical status, echocardiography, exercise performance, cardiovascular hospitalization, and survival after an average follow‐up of 36 months were analysed. Results Thirty patients (31.9%) displayed TD. TD was associated with lower tricuspid annular plane excursion (TAPSE) to pulmonary arterial systolic pressure PASP ratio (TAPSE/PASP) (P = 0.008), peak oxygen consumption (VO2 peak) (P = 0.03) and estimated glomerular filtration rate (P