An x-ray performed on a newborn infant shows enlargement of the left ventricle and left atrium as well as dilatation of the aoa. Echocardiographic studies demonstrate volume-overloading of the left ventricle. Cardiac auscultation reveals the presence of a continuous "machinery" murmur. Which of the following is the most likely diagnosis?
Atrial septal defect Patent ductus aeriosus Pulmonic stenosis Tetralogy of Fallot