Background: Patients with heart failure (HF) have been found to have cognitive deficits, but it remains unclear whether these deficits are associated with HF or with aging or comorbid conditions common in HF. Objectives: To 1) determine the types, frequency, and severity of cognitive deficits among patients with chronic HF compared to age- and education-matched healthy participants and participants with major medical conditions other than HF; and 2) evaluate the relationships between HF severity, age, and comorbidities and cognitive deficits. Methods: A sample of 414 participants completed the study (249 HF patients, 63 healthy and 102 medical participants). The HF patients completed measures of HF severity, comorbidity (multiple comorbidity, hypertension, depressive symptoms), and neuropsychological functioning. Blood pressure and oxygen saturation were assessed at interview; clinical variables were abstracted from records. Participants in the comparison groups completed the same measures as the HF patients except those specific to HF. Results: Compared to the healthy and medical participants, HF patients had poorer memory, psychomotor speed, and executive function. Significantly more HF patients (24%) had deficits in three or more domains. Higher (worse) HF severity was associated with more cognitive deficits; HF severity interacted with age to explain deficits in executive function. Surprisingly, men with HF had poorer memory, psychomotor speed, and visuospatial recall ability than women. Multiple comorbidity, hypertension, depressive symptoms, and medications were not associated with cognitive deficits in this sample. Discussion: Heart failure results in losses in memory, psychomotor speed, and executive function in almost one fourth of patients. Patients with more severe HF are at risk for cognitive deficits. Older patients with more severe HF may have more problems in executive function and men with HF may be at increased risk for cognitive deficits. Studies are urgently needed to identify the mechanisms for the cognitive deficits in HF and test innovative interventions to prevent cognitive loss and decline.