A 31-year-old male has a blowing murmur during S1 and a galloping additional heart sound. The murmur is best heard at the base of the heart. What is this condition?

The presence of a blowing murmur during S1, accompanied by a galloping additional heart sound, suggests the likelihood of mitral regurgitation. This condition involves backflow of blood from the left ventricle into the left atrium during systole, which is characterized by a holosystolic (blowing) murmur heard best at the apex, often radiating to the left axilla.

In this scenario, the key points indicating mitral regurgitation are the blowing murmur's timing relative to the heart sounds and the described location. A galloping heart sound can be associated with increased fluid volume or rapid ventricular filling, consistent with mitral regurgitation where the left atrium is exposed to increased volume from the regurgitant flow.

The other conditions listed exhibit different characteristics. Aortic regurgitation typically produces a diastolic murmur due to backflow from the aorta into the left ventricle, often best heard along the left sternal border. Tricuspid regurgitation would present with a holosystolic murmur best heard at the left sternal border, and aortic stenosis usually features a systolic ejection murmur best heard at the second right intercostal space