A 2-year-old child is brought to the physician for a routine examination. Physical examination shows a low- pitchedcardiac murmur. An echocardiogram shows the presence of ostium secundum, with a 1-cm defect. Which of the following abnormalities is most likely to be found in this child? (A) Pulmonary hypertension (B) Pericardial effusion (C) Left-to-right shunt (D) Mural thrombosis (E) Cyanos is