How Is A Heart Murmur Diagnosed In A Child?

Hi. My 4 yr old son has a heart murmur that didn t seem to show up till he was over a yr old. Then it became a very clear sign from then on. As in it s noticed right off the bat when a Dr. listens to his heart. He saw a pedatric cardiologist before he was 2. An ultra sound of the heart was done & came back clear. BUT the murmur continues to be loud, maybe louder. Should he have any more tests done?