54 days after the first vaccination with Moderna Covid-19 Vaccine, and 25 days after the second vaccination, at approximately 0730 on Day 1, a 52 year old male, height 175.2cm, weight 95.5kg, without significant medical history or prodrome, had an acute onset of dyspnea manifesting as a small sigh at intervals of 4-6 minutes, which increased in frequency to intervals of 2-3 minutes over the course of the day. At approximately 1400 he had a one minute episode of tachycardia >120 bpm. At 1515, his forehead became diaphoretic. He had neither chest pain nor a pericardial friction rub at any time. He went directly to the local emergency department. Additional information for Item 18:   Blood pressure at admission was 155/87, pulse 97, respiratory rate 22/minute, SpO2 98%, and Temperature 37.2. ECG at 1539 interpreted as: "NSR at 85, Lateral ST depressions; ST elevations in aVR, ischemia / Posterior wall MI".  ECG at 1541 showed: NSR at 82, unchanged from prior ECG. ECG at 1552 interpreted as: "Sinus tachycardia at 102, ST depressions remain in lateral leads but now also in V3 and V4; persistent ST elevations in aVR CW evolving posterior wall MI". PR depression in leads II and V4-6, and reciprocal PR segment elevation in aVR (pericarditis ECG Stage 1) Atypically for pericarditis, ST depression, rather than ST elevation, was present in leads V3-V6.  Owing to a working diagnosis of an evolving posterior wall myocardial infarction,  an emergent cardiac catheterization was performed, which demonstrated non-obstructive CAD and a small myocardial bridge. Initial laboratory values were notable for a white blood cell count of 11.89 K/mm3 (4.5 - 11.5), monocytes 1.1 K/mm3 (0.0 -1.0), 9.4% (2.0 - 9.0),  neutrophils 7.9 K/mm3 (1.5 - 6.6), 66.9% (40.0 - 75.0). Troponin was negative at admission and 18 hours later. D-Dimer was negative. Viral panels including SARS-CoV-2, Influenza A, Influenza B, and RSV were negative. He was admitted for overnight observation. On Day 2 an echocardiogram was normal with no effusion, and ECG was notable for the absence of PR depression and persistent ST depression in leads (PR segment normalization part of pericarditis ECG Stage 2)... His dyspnea persisted, with a moderate sigh every 1-2 minutes at rest. He was discharged with a presumptive diagnosis of coronary vasospasm or a pulmonary etiology, and told to follow up with his pmd. Over the next several days, his dyspnea was continuous and progressively worsened, and he had diaphoresis of the forehead every morning approximately 0900 until Day 20. Sleep remained normal. On Day 5 he was sighing deeply more than once per minute at rest, causing him distress, and ECG showed (?persistent ST depression in V4-6 with reciprocal changes in aVR). On Day 12, ECG showed T-wave inversion in V1-6 and ST depression in V3-6 (ECG Stage 3); a computed tomography of the chest was normal; and blood tests notable for normal monocyte count .57 K/microliter (0.0 - 0.8), normal CRP 2.15 (1.0-3.0), and an ANA titer of 1:80 (elevated) described as a speckled pattern, which is associated with several autoimmune diseases. Repeat echocardiography on Day 26 showed a small, generalized pericardial effusion and was otherwise normal. Cardiac MRI on Day 29 showed delayed gadolinium uptake. Pulmonary function tests on Day 38 were normal. Stress echocardiography on Day 44 was normal. Cardiac CT angiogram on Day 46was normal. The patient was diagnosed with pericarditis of unknown origin and started on aspirin 650 mg p.o. b.i.d. An ECG on Day 80 showed PR depression in II and V4-6, continued ST depression in II and V3-6, without T wave inversion (T wave normalization c/w ECG Stage 4). Symptoms progressively worsened from onset to nadir around Day 12, on which he had continuous moderate dyspnea upon awakening with severe dyspnea with mild exertion. Symptoms then generally improved until after Day 47, he began to have alternating periods of several days without symptoms followed by several days of  mild dyspnea.  Clinical symptoms resolved on Day 85.