Upper left arm vein was swollen and exposed; he had deep vein thrombosis in left arm; This spontaneous case was reported by a consumer and describes the occurrence of DEEP VEIN THROMBOSIS (he had deep vein thrombosis in left arm) in a 79-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 003A21A and 003A21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Cardiac assistance device user (pacemaker user).   On 07-Feb-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 07-Mar-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 25-Mar-2021, the patient experienced DEEP VEIN THROMBOSIS (he had deep vein thrombosis in left arm) (seriousness criterion medically significant). On an unknown date, the patient experienced VEIN DISORDER (Upper left arm vein was swollen and exposed). The patient was treated with RIVAROXABAN (XARELTO) for Adverse event, at an unspecified dose and frequency and Surgery (Pace maker installation to vein in Chest) for Deep vein thrombosis. At the time of the report, DEEP VEIN THROMBOSIS (he had deep vein thrombosis in left arm) and VEIN DISORDER (Upper left arm vein was swollen and exposed) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Blood test: antibodies detected (normal) antibodies detected.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   On 25Mar2021, upon performing a test, patient's left arm swollen twice of the size. Patient went to diagnostic procedure immediately and they came to conclusion that patient had deep vein thrombosis in left arm.  Concomitant medication included Blood Pressure medicine, Prostate medicine and Statin.  Company comment: This spontaneous  case concerns a 79-year-old male patient who is pacemaker user. with no relevant medical history reported, who experienced serious unexpected event of deep vain thrombosis of left arm. The events occurred approximately 18 days after the second dose of the Moderna COVID-19 vaccine .Initial symptom was swelling of left arm. Upon further diagnostic evaluation, the patient was diagnosed with deep vein thrombosis in the left arm.  Rechallenge was not applicable since the event occurred after the second dose so, no rechallenge was done and recurrence was not applicable. Patient's pacemaker suggests cardiovascular disorder which can be a possible confounder.  The benefit-risk relationship of drug is not affected by this report.; Sender's Comments: This spontaneous  case concerns a 79-year-old male patient who is pacemaker user. with no relevant medical history reported, who experienced serious unexpected event of deep vain thrombosis of left arm. The events occurred approximately 18 days after the second dose of the Moderna COVID-19 vaccine .Initial symptom was swelling of left arm. Upon further diagnostic evaluation, the patient was diagnosed with deep vein thrombosis in the left arm.  Rechallenge was not applicable since the event occurred after the second dose so, no rechallenge was done and recurrence was not applicable. Patient's pacemaker suggests cardiovascular disorder which can be a possible confounder.  The benefit-risk relationship of drug is not affected by this report.