Which flow abnormality produces a continuous murmur?

Comprehensive and Detailed Explanation From Exact Extract:

A continuous murmur is a heart murmur that occurs throughout both systole and diastole. Among the options, a ruptured sinus of Valsalva aneurysm produces a continuous murmur due to persistent flow between the aorta and a cardiac chamber (usually the right atrium or ventricle) during both systole and diastole.

Aortic regurgitation causes a diastolic murmur, mitral stenosis causes a diastolic murmur, and a muscular ventricular septal defect typically causes a holosystolic murmur but not continuous.

Ruptured sinus of Valsalva aneurysm causes a continuous shunting of blood, resulting in the characteristic continuous murmur, often described as “machinery-like.”

This clinical correlation is covered in the "Textbook of Clinical Echocardiography, 6e", Chapter on Aortic Root and Sinus of Valsalva Pathology【20:420-425†Textbook of Clinical Echocardiography】.