A 68-year-old man with a 40-pack-year smoking history and recent complaints of angina (sub-sternal chest pressure) upon exercising, collapsed while mowing his lawn. Paramedics arriving at the scene found him unconscious, not breathing, and without a pulse. CPR was successfully performed and Roger was transported to the hospital. An ECG was suggestive of an anterior wall myocardial infarction, and he was given an intravenous solution of tissue plasminogen activator (TPA). Elevated blood creatine phosphokinase (CPK) levels measured over the next 2 days confirmed the diagnosis. Coronary angiography was performed a week later, revealing the following results: Circumflex artery: 20% blocked
Right coronary artery: 15% blocked
Left anterior descending artery (LAD): 95% blocked

While listening to his heart with a stethoscope, you notice a high-pitched, blowing, systolic murmur, heard best directly under the left nipple. A review of Roger's medical records shows no prior history of a heart murmur. What is causing this new murmur?