DEAR DR. DONOHUE: I am a man, age 85, who is presently undergoing home treatment for congestive heart failure. I would like your opinion on cause, treatment and prognosis of the ailment. – F.M.

ANSWER: Congestive heart failure is the No. 1 reason why people over 65 are hospitalized. It’s the result of a heart that has gotten so weak that it cannot pump the normal volume of blood to the body and to the lungs.

The left ventricle – the left pumping heart chamber – propels blood to the entire body. When the left ventricle fails, blood backs up into the lungs. The lungs are saturated with fluid – they are congested. It is much like what happens in drowning.

The right ventricle – the right-sided heart chamber – receives blood from the body and pumps it into the lungs for oxygen. When this ventricle fails, blood backs up in the body, and the result is commonly seen as swollen ankles.

Both ventricles usually fail in tandem.

Inability to get enough air is a prominent symptom of congestive heart failure. Often, stricken people have trouble lying in bed because they become so short of breath in this position. They frequently waken during the night struggling to catch their breath.

Causes are many. An inadequate supply of blood to the heart muscle, a previous heart attack, leaking or narrowed heart valves and high blood pressure are a few of the conditions that lead to heart failure.

Drug treatments are many. ACE-inhibitor drugs such as Vasotec relieve the strain on a failing heart and permit it to beat more strongly. Beta-blocking drugs – Coreg is an example – also lessen the strain on the heart muscle. Diuretics (water pills) rid the body of excess fluid, and that eases the stress on the heart. The popular digitalis drug Lanoxin strengthens the heart’s pumping action. Salt restriction, weight reduction and a supervised exercise program are additional therapies for a failing heart.

You are being treated at home. That’s a good indication that your heart muscle is not severely impaired and that your prognosis is quite good.

The pamphlet on this topic answers the many questions left unanswered here. People can order a copy by writing: Dr. Donohue – No. 103, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.50 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: I have a son in his 30s who does not smoke and who runs 10 miles every day. He drinks one gallon of Diet Coke each day. I can’t believe this is good for him. Am I right to worry? – P.M.

ANSWER: A gallon? That’s 128 ounces (3.8 liters), far more than our daily fluid needs. This much Diet Coke delivers 490 mg of caffeine, an amount that must keep him more tightly strung than a just-wound clock. Diet Coke contains phosphoric acid, as do many soft drinks. Excessive amounts of phosphoric acid can lead to osteoporosis. Finally, people will want me to say that the amount of artificial sweetener in Diet Coke could get him in trouble. I am not convinced of that.

DEAR DR. DONOHUE: I run a low-grade fever, 99-100.5 F (37.2-38 C), every evening at bedtime. I wake up in three to four hours, and my temperature is back to normal. Any suggestions why this happens? – R.C.

ANSWER: Body temperature does not remain at 98.6 F (37 C) all day long. Calling that a “normal temperature” is somewhat of a myth. In the evening, body temperature hovers around 99.9 F (37.7 C), and in the early morning hours it dips to 97 F (36.1 C).

If you feel fine and if you have no symptoms or signs of illness, such as weight loss, cough or diarrhea, then you can retire the thermometer to its resting place in the medicine cabinet.

Your temperatures are not outside the norms. Stop taking it, or you are going to drive yourself crazy.

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.