Cardiac murmurs are abnormal heart sounds caused by turbulent blood flow through heart valves or openings. There are two types: functional murmurs caused by conditions like anemia without structural valve changes, and organic murmurs caused by structural valve abnormalities. Murmurs can be systolic (early, mid, or late), diastolic (early, mid, or late), or continuous. They are classified based on when they occur in relation to the heart sounds.