21 year-old man with a 40-pack-year smoking history and recent complaints of angina upon exercising, collapsed while running a marathon. Paramedics arriving at the scene found him unconscious, not breathing, and without a pulse. CPR was successfully performed and Micheal 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 3 days confirmed the diagnosis. Coronary angiography was performed a week later, revealing the following: Circumflex artery: 25% blocked
Right coronary artery: 30% blocked
Left anterior descending artery (LAD): 95% blocked
("Anterior intraventricular artery")

Required:
a. What is a myocardial infarction?
b. What is the cause of Micheal Lee's myocardial infarction?