DEAR DR. DONOHUE: I have congestive heart failure. Please write about how it affects a person. I breathe through my mouth at night. Is that part of it? – L.O.

ANSWER: When it comes to naming one of mankind’s most prevalent and most disabling illnesses, congestive heart failure is at or near the top of the list.

It is an inability of the heart to pump enough blood to provide the oxygen and energy a person needs for ordinary activities such as walking, making a bed, running a vacuum or climbing stairs.

An old heart attack that leaves a large scar in heart muscle, a poor blood supply to the heart in people with clogged heart arteries, inadequately treated high blood pressure, and faulty heart valves are some of the reasons why the heart cannot pump blood as it should.

The result is a pooling of blood in the heart and a backup of blood into the lungs and body. In lungs, the backed-up blood oozes fluid into the air sacs. It is very much like what happens to people who drown. Their lungs are filled with fluid. Oxygen cannot pass into the blood. People are left gasping for air. Lying down to sleep increases the fluid volume in the lungs. So bedtime is a time of breathlessness. Often, congestive heart patients wake from sleep because they feel they are suffocating. They bolt from bed and throw open a window in the vain hope of getting more air. Mouth breathing at night, however, is not an indication of heart failure.

Diuretics – water pills – rid the body of excessive fluid. Other medicines relieve the strain on the heart, allowing it to pump with greater ease. Digoxin, one of the digitalis drugs, is often called on to strengthen heart contractions. A low-salt, low-fat and low-cholesterol diet is always an ingredient in a treatment recipe. Alcohol should be consumed sparingly, if at all. It can depress the strength of heart muscle.

DEAR DR. DONOHUE: My grandson, 16 years old, has Marfan’s syndrome. My husband and I know nothing about it. It is supposed to be a genetic disease, but neither my daughter nor son-in-law has it. How can it be genetic? – C.C.

ANSWER: A gene change is the cause of Marfan’s syndrome. However, one-quarter of Marfan patients do not have parents who have the gene. The gene change took place when they were developing embryos in their mother’s uterus.

Marfan patients tend to have long arms and legs and the slender, elongated fingers of a concert pianist. The lens of their eye can slip out of place. They might have leaky heart valves. Their aortas are often fragile and prone to tear apart. The aorta is the body’s largest artery, the one into which the heart pumps blood for distribution to all other body arteries.

The picture I painted is grim. That is certainly not the case for most Marfan patients. The majority lead active, healthy and long lives. Once their doctors are alerted to the problem, they keep close tabs on these people’s health. One way is a yearly echocardiogram that can show any dangerous changes in heart valves or the aorta. If there are such changes, they can usually be surgically repaired.

The best thing I can do for you is put you in touch with the National Marfan Foundation, whose number is 1-800-862-7326 and whose Web site is www.marfan.org.

DEAR DR. DONOHUE: My 10-year-old daughter, an only child, has always been extremely sensitive and overly moody. Her mood swings, crying jags and hopelessness have escalated to a point that’s more than our family can bear. I am a well-educated person who has bipolar illness. Is my daughter too young to be evaluated and treated for a depressive disorder? – L.G.

ANSWER: Your daughter is not too young to suffer from depression or to be treated for it. You should arrange for an interview with a mental-health professional right away.

For readers, bipolar illness is a condition where people swing from moods of utter despair to those of abnormal elation. Depression and bipolar illness are strongly linked to inheritance. Both are treatable.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.