HEART ATTACK; HIGH FEVER; This spontaneous report received from a patient concerned a male of unspecified age. The patient's height, and weight were not reported. The patient's concurrent conditions included heart disorder ("born-in" heart issues). The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin, and batch number were not reported) dose was not reported, administered on 10-MAR-2021 12:30 for prophylactic vaccination. The batch number was not reported and has been requested. No concomitant medications were reported. On 10-MAR-2021 at 19:30, the patient unexpectedly broke out into a very cold sweat, high fever, extreme stomach nausea, and his heart raced to levels he had never felt. The patient could not walk and could barely respond verbally to his fiance for help. The patient was admitted to the hospital. The patient was taken on a wheel chair and was attended to immediately because of the severity of his condition. The emergency room doctors and nurses thought the patient was having a heart attack, as did he. The patient informed emergency room doctors and nurses that he had been given covid-19 vaccine ad26.cov2.s earlier in the day. After several hours of testing including electrocardiogram, computerized tomography scans, intravenous and constant blood pressure monitoring, it was determined that the patient should be transported to a hospital that was better equipped to service his apparent condition. The hospital staff was concerned about a possible heart attack and not knowing the patient's history or having the equipment and staff to service this, they decided the patient needed to be taken to a hospital that specializes in heart events. Having had cardiology care in the past for "born-in" heart issues, the patient wanted to be transported to Medical Center where all of his doctors were residences. According to the patient, they had a fabulous team of world renowned cardiology experts from Cardiology. The hospital staff at the Hospital offered to send the patient to Hospital. Both hospitals were about equal distance from the Hospital. The patient obviously wanted to go to where his doctors were and who know him personally for almost his whole life. According to the patient, the staff at the Hospital were fantastic, and as they stated to him verbally, probably saved his life. An Ambulance ride followed at about 3:00 AM on 11-MAR-2021 arrived at approximately 04:30 at medical center. The patient's cardiologist's covering doctors met him on the cardiology floor to immediately begin monitoring and performing every test at their disposal. The patient also informed the cardiology team that he had received the covid-19 vaccine ad26.cov2.s vaccine on 10-MAR-2021 (Wednesday) afternoon. According to the patient, their eyes lit up immediately believing that the vaccine might had caused this. After almost 2 days and countless tests, blood screens, monitoring and consultation, the patient was released late afternoon on 12-MAR-2021 from hospital after being stabilized to a normal level. According to the patient's doctors, the only cause of these events could have been the covid-19 vaccine ad26.cov2.s vaccine. According to the patient, the severity of this events were only curtailed by the excellent care he received from both of his hospital visits and the almost 2 day stays. The patient's doctors had instructed him to stay close to home and continue to monitor his condition in the upcoming weeks because no one knows if these events could happen again. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient recovered from high fever, and heart attack on 12-MAR-2021. This report was serious (Hospitalized and Other Medically Important Condition).; Sender's Comments: V0: 20210333833- Covid-19 vaccine ad26.cov2.S- Heart Attack. This event is considered not related. The event has a compatible/suggestive temporal relationship, is unlabeled, and has unknown scientific plausibility. There are other factors more likely to be associated with the event than the drug. Specifically: MEDICAL HISTORY. 20210333833-covid-19 vaccine ad26.cov2.s- high fever. This event is labeled and is therefore considered potentially related.