Stage 4 heart failure diagnosis. how can it be stage 4 with limited symptoms and no symptoms at rest ?

Good question: Diseases staging by the doctors are based on certain diagnostic points. These stages might not exactly co-relate with the severity of active symptoms the patients might encounter. Acuity of symptoms makes patients sicker. For example a person with stage 2 heart failure can be sicker when he/she has exacerbation, than who has stable stage 4 disease. Stage 4 does not always mean terminal.