Chest Pain in a 37-year-old man

A 37-year-old man presented to the emergency department with chest pain of 2 days’ duration. The pain was heavy in character, intermittent, and made worse by deep inspiration and lying flat.

The man had no shortness of breath and had been actively working as a gardener until the onset of the pain. He was an active smoker, and his father had had a myocardial infarction at the age of 52 years. He did not have hypertension.

What is the diagnosis?