If you have a history of heart disease, heart murmur or rheumatic fever, consult with your cardiologist before conceiving to see if there are any special medical precautions you should take.

That's because pregnancy places additional demands on your body's circulatory system and alters the way it operates so more blood can pass through the placenta to the baby. Among the more important changes is a dramatic increase in "cardiac output". This is the volume of blood your heart pumps each minute. Cardiac output increases by 30% to 40% during pregnancy.

These physiological changes that affect all pregnant women make your heart work harder. So, it's wise to get an expert opinion on what the added load might mean to your pregnancy.

Some mothers-to-be whose hearts were normal before pregnancy may develop cardiac disorders such as:

• A heart murmur (an unusual heart sound that usually doesn't indicate a problem during pregnancy but in rare cases can signal a heart valve problem)
• A fast, slow or irregular heartbeat (arrhythmia, another problem that usually doesn't require special treatment), or
• High blood pressure.

Here's a more detailed look at some specific heart conditions and how they might affect you during pregnancy:

• Congenital heart disease. Most women born with an abnormality of the heart or its major blood vessels can safely have children. Before conceiving, however, you'll need evaluation by a cardiologist to determine the type and severity of the defect to accurately access any potential risks that pregnancy may pose. This examination probably will include tests such as an electrocardiogram (ECG), chest X-rays (notify the doctor before the X-rays are taken if there is any chance you may already be pregnant), an echocardiogram, (an ultrasound strictly to detect heart valve or other abnormalities), and/or an exercise stress test to measure your heart rate as you move at various speeds on a treadmill.
  
  Another point to keep in mind is that babies born to women with congenital heart disease have a higher risk of having some form of heart abnormality. A pediatric cardiologist can evaluate your unborn baby's heart development though a fetal ultrasound examination once you are 17 or more weeks pregnant.



• Pulmonary hypertension. Pregnancy is not advised if you have pulmonary hypertension (not to be confused with high blood pressure), a condition causing very high blood pressure in the blood vessels of the lungs and associated with a high risk of dying during pregnancy.



• Aortic valve stenosis. Another heart abnormality that creates a significantly elevated risk of maternal and/or fetal death during pregnancy is uncorrected severe narrowing of the aortic valve. This condition prevents blood being pumped by the heart from entering the aorta.
  
  
• Coarctation of the aorta. In this rare condition, there is a localized narrowing of the artery, which reduces blood supply to the lower part of the body. If uncorrected, it too creates a high maternal and fetal risk.



• Uncorrected cyanotic heart deformities. These cause the skin to turn bluish as the result of too much oxygen-poor hemoglobin in the blood. In some cases, such problems can be surgically corrected, permitting pregnancy.



• Rheumatic heart disease. This condition results from a streptococcal infection called rheumatic fever that may cause scarring of one or more of the heart valves. Such damage, which only may become evident years after the original disease, impedes the injured valves from opening and closing normally, obstructing the flow of blood. In most cases, you'll still be able to have a baby, but will need monitoring during pregnancy to make sure your heart is not being strained excessively.



• Other conditions. If you have some forms of arrhythmia (an irregular heartbeat), cardiomyopathy (disease of the heart muscle) or some other cardiac disorder, you'll face a higher risk of heart ailments during pregnancy than a woman free of these conditions. You also need to know that some heart medicines are hazardous to a developing baby. Anticoagulant or blood-thinning medications such as Coumadin and dicumarol, which sometimes are prescribed for people with an artificial heart valve or who have other conditions that may cause them to be at risk for blood clots, are also potentially harmful to an unborn child.

Heparin, another anticoagulant drug that's given by injection, is safe for use when you're pregnant, according to the American Heart Association. So it may be a good alternative if you need this type of medicine. Along with discussing your medications with your doctor, you'll want to ask what sort of monitoring is most appropriate for your case during pregnancy.

For more information, send a stamped self-addressed envelope to the American Heart Association, National Center, 7272 Greenville Ave., Dallas, TX 7523, and ask for their booklet, "Safeguarding Your Heart During Pregnancy."