29th September is World Heart day A healthy heart produces two distinct sounds lub dub. The 'lub' is a sound caused by the mitral and tricuspid valves closing at the beginning of a systole (contraction). The 'dub' is the snapping shut of pulmonic and aortic valves denoting the end of the systole.Here is a demonstration of normal heart sounds from the University of Washington Department of Medicine. Heart murmurs A heart murmur is an unusual sound that is heard during a heartbeat. Murmurs can be so faint that they are barely noticeable or considerably loud that they sound like whooshing.