Перевести. when we listen to the heart we can hear two sounds. the third sound is also heard in some young persons before the age of 30. the first heart sound is the longest one. it is heard at the moment of contraction of the ventricles when the atrio-ventricular valves close. the second sound lasts for a shorter period of time. it is heard at the moment when the pulmonary and aortic semi lunar valves close. the third heart sound is heard when the blood is passing from the atria into the ventricles. the first and the second cardiac sounds are heard over all the portions of the heart and often over the large vessels. the first heart sound is greater over the surface of the ventricles and it is the greatest over the surface of the mitral and tricuspid valves.