After the vaccination, and while in the hospital, she was diagnosed with a blood clot in the left atrium the size of a golf ball; Reported she was diagnosed with a spontaneous peptic ulcer bleed; Stated that she feels like she is "sitting on a powder keg"; This spontaneous case was reported by a patient (subsequently medically confirmed) and describes the occurrence of ATRIAL THROMBOSIS (After the vaccination, and while in the hospital, she was diagnosed with a blood clot in the left atrium the size of a golf ball) and PEPTIC ULCER HAEMORRHAGE (Reported she was diagnosed with a spontaneous peptic ulcer bleed) in a 73-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 022M20A and 211M28-9) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Heart failure (7 years ago- consumer reported it resolved on its own but was placed on Entresto at that time) in 2014 and Arterial stent insertion (Left atrial appendage closure device to treat atrial fibrillation and prevent clots) in 2019. Concurrent medical conditions included Arthritis, Cardiac disorder NOS (Body aches), Headache, Fluid imbalance (Fluid in feet), High cholesterol, Hypotension and Pain. Concomitant products included CARVEDILOL (COREG), HCTZ, VITAMIN C [ASCORBIC ACID], ATORVASTATIN CALCIUM (LIPITOR), ACETYLSALICYLIC ACID (BABY ASPIRIN) and PARACETAMOL (TYLENOL) for an unknown indication.   On 03-Feb-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 02-Mar-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 24-Mar-2021, the patient experienced ATRIAL THROMBOSIS (After the vaccination, and while in the hospital, she was diagnosed with a blood clot in the left atrium the size of a golf ball) (seriousness criteria hospitalization prolonged and medically significant). On an unknown date, the patient experienced PEPTIC ULCER HAEMORRHAGE (Reported she was diagnosed with a spontaneous peptic ulcer bleed) (seriousness criterion medically significant) and FEELING ABNORMAL (Stated that she feels like she is "sitting on a powder keg"). The patient was hospitalized from 24-Feb-2021 to 12-Mar-2021 due to ATRIAL THROMBOSIS. At the time of the report, ATRIAL THROMBOSIS (After the vaccination, and while in the hospital, she was diagnosed with a blood clot in the left atrium the size of a golf ball), PEPTIC ULCER HAEMORRHAGE (Reported she was diagnosed with a spontaneous peptic ulcer bleed) and FEELING ABNORMAL (Stated that she feels like she is "sitting on a powder keg") outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 06-Feb-2021, Echocardiogram: results are not mentioned (Inconclusive) Results are not mentioned.         The patient stated that she initially was being cared for by a small, local hospital but was transferred to a larger hospital. The patient reported that she has never had any blood clots until now.   Treatment for the event included apixaban (twice daily).  The patient received both scheduled doses of mRNA-1273 prior to the event; therefore, action taken with the drug in response to the event is not applicable.   This case was linked to MOD-2021-075865 (Patient Link).; Sender's Comments: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.