A continuous murmur, heard throughout systole and diastole, is most characteristically caused by a patent ductus arteriosus (PDA). PDA represents persistent communication between the aorta and pulmonary artery, allowing continuous blood flow during both phases of the cardiac cycle.

Ventricular septal defect usually produces a holosystolic murmur. Concomitant aortic stenosis and mitral regurgitation cause separate murmurs but not continuous. Ebstein anomaly with atrial septal defect typically produces murmurs related to tricuspid regurgitation or ASD but not a continuous murmur.

This clinical correlation is detailed in the 'Textbook of Clinical Echocardiography, 6e', Chapter on Congenital Heart Disease and Murmur Etiologies20:420-425Textbook of Clinical Echocardiography.