Ans. (a) Acute pericarditis.The tracing reveals sinus rhythm at approximately 75 beats/ min. The PR interval is prolonged to 200 milliseconds consistent with borderline first-degree AV block. The QRS axis and intervals are normal.ST elevations with concave upward morphology are seen in I and aVL, II and aVF, and V2 through V6. No Q waves are present. Furthermore, subtle PR-segment depression is seen in leads I and II. The differential diagnosis for ST-segment elevation includes, among other things, acute myocardial infarction, pericarditis, and left ventricular aneurysm. In this case, the upward concavity of the ST segment, the PR-segment depression, the lack of Q waves, and the diffuse nature of the ST-segment elevation in more than one coronary artery distribution make pericarditis the likely etiology. Patients with pericarditis will complain of chest pain, typically described as sharp and pleuritic. Radiation is to the trapezius ridge. The pain is improved with sitting up and leaning forward and worsened by leaning backward.