An 8-month-old child's examination revealed a loud systolic murmur over the entire cardiac region with an epicenter in the III-IV intercostal spaces to the left of the sternum and a systolic tremor, the second tone over the pulmonary artery is of increased volume. Blood pressure - 110/70 mm Hg. There are no complaints, X-ray shows that the size and shape of the cardiac shadow are without changes What is the most likely diagnosis in this case?