The left border is formed by the arch of the aorta (constituting a prominence known as the aortic knob, or knuckle), pulmonary trunk, left auricle, left ventricle, and extrapericardial
[dartmouth.edu]
Patients can be asymptomatic, but they may experience chest pain, myocardial ischemia, emboli, arrhythmia, and sudden death.
[ncbi.nlm.nih.gov]