A heart murmur refers to a sound heard by a doctor listening to the heart with a stethoscope that often is subtle or soft although sometimes can be quite loud. While it is often not serious, it can be due to a heart defect or improperly functioning heart valve. Blood moving through heart valves that are working properly can sometimes create a murmur which is not due to any serious cardiac problem.  This can also occur if the heart is working vigorously in non-cardiac conditions such as pregnancy, anemia or an overactive thyroid.  However, significant heart valve abnormalities or structural heart defects may cause a heart murmur. Louder murmurs can be due to more serious valve problems, but some of the most significant structural heart problems can cause very faint murmurs.  Listening to a patient’s heart sounds over time allows the cardiologist to determine the progression of the underlying problem, especially in conjunction with other signs on the exam, changes in a patient’s symptoms, and other findings from testing.  Ultimately, echocardiography, or an ultrasound of the heart, is the test of choice to help confirm structural heart disease or heart valve disease and determine whether a heart abnormality is changing, in conjunction with patient symptoms.