In some adults, slightly hardened or oversized heart valves may cause the heart's circulating blood to make noises referred to as 'murmurs.' Hardened or narrowed heart valves may not be able to open completely, forcing blood to move through a smaller-than-normal opening. Loose, oversized heart valves may not be able to close completely, allowing blood to leak backwards from one chamber to the other. Pregnancy, fever, anemia and thyrotoxicosis (thy-row-tox-ih-KO-sis), are all conditions that can temporarily cause such a murmur. Some murmurs may not be related to valve dysfunction, but can be due to blood leakage through a hole in the heart wall. Murmurs are classified as either diastolic (die-ah-STALL-ik) or systolic (sis-TALL-ik). When the sound occurs as the heart muscle is relaxing between beats, it's called a diastolic murmur. If it happens during the heart's contraction phase, it's known as a systolic murmur. Mitral (MY-trahl) valve prolapse, or MVP (M-V-P), is a fairly common cause of systolic murmur. In MVP, enlarged valves between the upper and lower left chambers of the heart close unevenly and collapse back into the upper atrium (AY-tree-um) chamber. Thus, the blood is not completely emptied from the upper atrium to the lower ventricle (VEN-trik-uhl) chamber during pumping. Instead, some blood leaks back into the atrium and causes a murmur. MVP has several other names: click-murmur, Barlow's syndrome, balloon mitral valve syndrome, or floppy valve syndrome. Depending on the amount of blood leakage and loudness of the murmur, these conditions may or may not require treatment. If you're concerned about your heart health or have any questions about heart murmurs, contact a healthcare provider.