DEAR DR. DONOHUE: I am 34 and have been very athletic all through my life. I still play basketball and run close to 30 miles every week.

As an employment requirement, I had to have a physical exam that included a chest X-ray. The X-ray shows that my heart is enlarged, and I have to follow up with a doctor. I have no symptoms. Am I in deep trouble? – G.M.

ANSWER: Not all heart enlargement is a sign of bad health. Hearts enlarge for both good and bad reasons. Athletes have larger-than-normal hearts. The heart is a muscle and, like any muscle, exercise makes it grow. Your heart enlargement might be nothing more than a consequence of your athletic lifestyle.

Bad things cause heart enlargement too. Heart failure is one of them. The heart becomes so flabby that it can’t pump out all the blood it contains.

The backup of blood in the heart stretches it out of shape. On an X-ray it is bigger than normal. Heart failure for a 34-year-old fitness devotee is not at all likely. Scratch this worry off the list.

Untreated high blood pressure is another cause of big hearts. The heart compensates for high pressure by growing larger. However, there comes a point of diminishing returns and an ever-enlarging heart eventually loses its effectiveness. High blood pressure is a possible cause for your enlargement, but not a probable one.

Viral infections of the heart dilate the heart, and it appears enlarged on an X-ray. Heart viral infections most often make a person quite sick and frequently leave the person short of breath after the infection has quieted down. This is another improbable cause of your enlargement.

Heart valve problems can also lead to large hearts. Valve problems most always cause murmurs, and you have never been told you have one, have you?

I feel safe in predicting the doctor will find nothing wrong with your heart.

DEAR DR. DONOHUE: The nurse in my doctor’s office called me in a frenzy to tell me I have hepatitis A and B and should come in as soon as possible. She said my blood tests show I have antibodies to those viruses. I am a just-returned missionary to Africa. Before going, I was immunized with the hepatitis A and B vaccines. I tried to explain this to her, but she insists I make an appointment. I don’t believe I need to. Do you? – P.R.

ANSWER: I don’t believe you need to see the doctor either. But I can’t give you the 100 percent reassurance that I would like to from this distance and from only a letter’s information. So see the doctor. It will be one of the briefest office visits you have ever had.

Both of the vaccines are intended to spur the body to produce antibodies against the germ each was made for. Antibodies are huge proteins that prevent germs from taking hold in the body and multiplying. Most likely you will have them for the rest of your life. They’re doing you good.

I have another thought. Why not speak to the doctor on the phone? That could save you an office visit.

DEAR DR. DONOHUE: Can a person with a herpes infection of the lips pass the infection to a partner through oral sex? Occasionally I break out with a cold sore. – T.C.

ANSWER: Herpesvirus type 1 causes cold sores (fever blisters). Herpesvirus type 2 is the type most responsible for genital infections.

However, a person with a cold sore can transmit the type 1 virus to the genitals through oral sex. The resulting outbreak looks just like an outbreak of the herpesvirus type 2 in that location.

In the same way, a person with a type 2 infection of the genitals, can pass the virus to a partner’s lips through oral sex. It appears like a typical cold sore.

DEAR DR. DONOHUE: Is there such a thing as having too much semen? – S.P.

ANSWER: I have never heard of the condition, if it truly does exist.

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. Readers may also order health newsletters from www.rbmamall.com.