Atrial flutter; Chest mass NOS; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FLUTTER (Atrial flutter) in a 72-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.    Co-suspect product included non-company product IBRUTINIB (IMBRUVICA) for Chronic lymphoid leukemia.    The patient's past medical history included Heart rate low in September 2021, Surgical site infection in 2001 and Hip replacement (SURGICAL SITE GOT INFECTED WHICH RESULTED IN KIDNEY DAMAGE) in 2001. Concurrent medical conditions included Crohn's disease since 1978, Glaucoma, Hypertension NOS, Arteriosclerosis since September 2021, Kidney disorder since 2001 and Chronic lymphoid leukemia.   In October 2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 17-Dec-2021, the patient started IBRUTINIB (IMBRUVICA) (Oral) 420 milligram once a day. On an unknown date, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On an unknown date, received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. In 2021, the patient experienced ATRIAL FLUTTER (Atrial flutter) (seriousness criteria hospitalization and medically significant). In 2022, the patient experienced MASS (Chest mass NOS). The patient was hospitalized for 7 days due to ATRIAL FLUTTER. At the time of the report, ATRIAL FLUTTER (Atrial flutter) had resolved and MASS (Chest mass NOS) was resolving.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In 2021, Electrocardiogram: abnormal abnormal. In 2022, Cardiac stress test: normal normal. In 2022, Echocardiogram: normal normal. On an unknown date, Positron emission tomogram: result were not provided Result were not provided.         No concomitant medication details were reported.  In 2021 the patient experienced atrial flutter. In 2022 the patient experienced knot on chest. On an unknown date, atrial flutter resolved. Moderna covid-19 vaccine was also considered suspect.   In oct -2021, the patient got the covid booster and had an episode of atrial flutter then went to an urgent care. After EKG results, they sent the patient to the hospital via ambulance, where patient was admitted for seven days. Patient believed that there was a correlation between the timing of the booster and the atrial flutter. In 2022, follow up stress test and echo were normal for patient.  No treatment medication details were reported.  Causality for IMBRUVICA(IBRUTINIB): the reporter causality for the event of atrial flutter and knot on chest was not reported.  Company Comment: This is a Spontaneous case concerning a 72-year-old male patient, with relevant medical conditions of hypertension, chronic lymphoid leukemia, arteriosclerosis and kidney disorder, who experienced the unexpected and serious (due to hospitalization and medically significant) AESI of Atrial flutter, which occurred after the third dose of mRNA-1273 vaccine. Patient went to an urgent care, and after electrocardiogram results, he was sent to hospital via ambulance, where he was admitted for seven days. In 2022, follow up stress test and echocardiogram were normal per patient. Co-suspect product included non-company product Ibrutinib (Imbruvica) for chronic lymphoid leukemia, received approximately 2 months after the third dose of mRNA-1273 vaccine. No information disclosed about treatment received. Medical conditions of hypertension, chronic lymphoid leukemia, arteriosclerosis and kidney disorder, remain confounders for Atrial flutter. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.; Sender's Comments: This is a Spontaneous case concerning a 72-year-old male patient, with relevant medical conditions of hypertension, chronic lymphoid leukemia, arteriosclerosis and kidney disorder, who experienced the unexpected and serious (due to hospitalization and medically significant) AESI of Atrial flutter, which occurred after the third dose of mRNA-1273 vaccine. Patient went to an urgent care, and after electrocardiogram results, he was sent to hospital via ambulance, where he was admitted for seven days. In 2022, follow up stress test and echocardiogram were normal per patient. Co-suspect product included non-company product Ibrutinib (Imbruvica) for chronic lymphoid leukemia, received approximately 2 months after the third dose of mRNA-1273 vaccine. No information disclosed about treatment received. Medical conditions of hypertension, chronic lymphoid leukemia, arteriosclerosis and kidney disorder, remain confounders for Atrial flutter. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.