An 8-year-old male neutered domestic shorthair cat is presented with a 1-month history of progressive exercise intolerance, panting, anorexia, weight loss and vomiting. On physical exam there is moderate cyanosis and a jugular pulse. On chest auscultation there is a systolic murmur loudest on the left side between the 5th and 6th intercostal space. A DV chest radiograph looks like the image below. What is the diagnosis?