Hi Marie,
A murmur can be caused by several things going on in the heart; a leaky valve, a narrowed valve (think about blowing through a tightened space like a whistle), or increased blood flow through certain areas of the heart (in young, otherwise healthy patients these are called "flow murmurs" and are usually normal). Murmurs vary in their sound and intensity depending on what specifically is causing the sound and where. When doing an ultrasound of the heart, the machine is able to pick up murmurs and flow through the heart and its valves much more effectively than a stethoscope can. It is not uncommon that providers are unable to hear murmurs from the chest using a stethoscope even though a leaky valve or narrowed valve may be present. The worse the "leakiness" is, usually the louder the murmur is, making it less likely to miss with a stethoscope. So the short answer to your questions is yes, there can still be leaky valves without being able to hear a murmur on exam. Hope that helps!
Marie,
This is a common source of confusion for patients.
It is helpful to define the terms we are using. A murmur is a musical sound heard through the stethoscope as a result of turbulent blood flow. It is a physical exam finding, not necessarily always pathologic (due to disease).
Mitral valve prolapse is a specific disease of the heart valves or a type of valvular heart disease. Just like all murmurs are not due to disease, in some patients valvular heart disease can not be detected on physical exam (no murmur is heard).
An echocardiogram has higher sensitivity (ability to pick up disease) than physical exam. This is why it is possible that the echo tech could detect valvular heart disease (she did not detect a murmur unless she actually listened to your heart with a stethoscope) while your physical could not detect a murmur.
Mitral valve prolapse can sometimes be difficult to auscultate (hear with a stethoscope). Often times physicians ask patients to "bear down like they are having a bowel movement", called a Valsalva manuever, to bring out the murmur.
Thank you for your question!
-Dr S