KnowraHeart soundsLinked fromLinked fromThe 3 pages that link to Heart sounds, each with the reason it gives.All 3Related 3Cardiac cycleRelated: The first and second sounds mark key valve events within the cycle.Systole (cardiac physiology)Related: The first heart sound marks closure of the atrioventricular valves near systole's onset.René LaennecRelated: Auscultation extended the same listening approach from the lungs to the heart.