Background Clinician-assigned New York Heart Association (NYHA) class is an established predictor of outcomes in heart failure. This study aims to test whether patients' self-assessment of functional status by NYHA class predicts hospital admissions, quality of life, and mortality. Methods and Results This was an observational study within a randomized controlled trial. A total of 293 adult patients diagnosed with heart failure were recruited after an emergency admission at 3 acute hospitals in Norfolk, UK. Outcome measures included number of emergency admissions over 6 months, self-assessed quality of life measured with the Minnesota Living with Heart Failure questionnaire (MLHFQ) and EQ-5D at 6 months, and deaths up to 20 months' follow-up. Patients were grouped into 3 NYHA groups (I/II, III, and IV) based on patients' self-assigned NYHA class (SA-NYHA). A Poisson model indicated an increased readmission rate associated with higher SA-NYHA class (adjusted rate ratio 1.21; 95% CI 1.04–1.41; P = .02). Higher SA-NYHA class at baseline predicted worse quality of life at 6 months' follow-up (P = .002 for MLHFQ; P = .047 for EQ-5D), and was associated with higher mortality rate (adjusted hazard ratio 1.84; 95% CI 1.10–3.06; P = .02). Conclusions SA-NYHA class is predictive of hospitalization, quality of life, and mortality among patients with heart failure.