The purpose of this study is to determine how the immune system changes with aging and makes influenza a more serious illness in older people. Influenza vaccination not only can protect people from getting the flu but also can lessen the severity of the illness. This is particularly true for people with congestive heart failure (CHF). This research may provide information that could eventually lead to a new laboratory test that will predict how effective vaccination is for preventing influenza illness in older people. Volunteer participants in this study will include the following groups: 1) healthy young adults 20 - 40 years old; 2) older adults, 60 years and older, without a history of CHF; 3) older adults, 60 years and older, with a history of CHF. All study participants will be vaccinated with the current preparation of inactivated influenza vaccine. A small amount of blood will be drawn before each vaccine and at 4, 10, and 16-20 weeks afterward.