The imaging characteristics of ventricular septal defects are as follows:

1. Small defects: Normal cardiac silhouette, or left ventricular hypertrophy, with mild pulmonary congestion.

2. Medium defects: Left ventricular hypertrophy or biventricular hypertrophy, enlarged pulmonary artery segment, smaller aortic knob.

3. Large defects: Both ventricles enlarged, left atrium enlarged, prominent pulmonary artery segment, significant pulmonary congestion. When pulmonary hypertension with right-to-left shunting occurs, the pulmonary artery segment is markedly prominent, but the lung fields are clear, and the heart shadow is smaller than before.