A patent ductus arteriosus causes a continuous murmur since there is a constant pressure gradient in both systole and diastole forcing blood from the aorta into the pulmonary artery. The normal ...

prolonging the patency of the ductus arteriosus (PDA). [16] The murmur associated with a PDA is best heard at the upper left sternal border and is described as a machinery-like murmur. The ...