Heart murmurs are a result of turbulent blood flow that can be heard. They are often caused by defective heart valves that are either leaking or narrowed. Heart murmurs can also be caused by conditions such as anemia, pregnancy, fever, and thyrotoxicosis (overactive thyroid gland). Sometimes people get heart murmurs from various random blood flow characteristics with no clinical significance.

There are 2 main kinds of heart murmurs - diastolic and systolic. Diastolic heart murmurs occur when the heart muscle relaxes between beats. Systolic murmurs occur when the heart muscle contracts and are graded on how loud they are.