HEART RATE INCREASED; HEART RATE UNSTABLE; FELT LIKE FIGHTING COLD OR FLU; RESPIRATORY TRACT CONGESTION; VOICE NOT NORMAL; FATIGUED; This spontaneous report received from a patient concerned a 63 year old white (non-Hispanic or Latino) male. The patient's height, and weight were not reported. The patient has not been on any medication and had not seen a doctor for years as he had been feeling really good for years until the last 7-10 days. The patient received Covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin not reported, batch number: 203A21A, expiry: UNKNOWN) dose was not reported, 1 total dose administered on 08-APR-2021 in the late afternoon to left arm for prophylactic vaccination . No concomitant medications were reported.  The patient used fitbit and his resting heart rate was high 50s or into 60s beats per minute.  On APR-2021, the patient reported that he had been fatigued the first 2 days by following the shot (laid down and watched tv), then went back to normal. Starting one week to 10 days ago, on MAY-2021, his resting heart rate increased to in the 90s beats per minute which could not get below that.  On 11-MAY-2021, the patient's heart rate became totally unstable and he had to go to emergency room at 11:00 with heart rate spiking in the 190s beats per minute. His heart rate was in the 180-190s beats per minute, but it was bouncing all over (for example 120, 90, then 190s beats per minute.) Heart rate would bounce around within seconds of each other. He was transferred into hospital and admitted to hospital on 11-MAY-2021 at 22:00 until 12-MAY-2021 at around 17:00. The patient was hospitalized for two days also was put on medications (blood thinner, beta blocker and another medication) while in hospital. It was reported that in hospital they were going to use paddles to shock, but heart rate stabilized on it's on so he was able to be discharged. On 12-MAY-2021, while in hospital heart rate stabilized to around 74 beats per minute. If he moved around at all heart rate went back into the 90s beats per minute. He told that this never happened to him before. On 13-MAY-2021, the patient reported that heart rate high around 80s to 90s beats per minute while resting and over 100 beats per minute when moves around. On MAY-2021, the last 7-10 days he started feeling fatigued, like fighting some kind of cold or flu (but didn't have either) and chest congestion, voice was not normal. He felt like having vaccine response or immune response. This was still going on. Laboratory data included: COVID-19 virus test (NR: not provided) negative (units unspecified), and Heart rate (NR: not provided) 190s beats per minute. Treatment medications (dates unspecified) included: metoprolol tartrate(Lopressor), and apixaban (Eliquis). The action taken with Covid-19 vaccine ad26.cov2.s was not applicable. The outcome of heart rate increased, felt like fighting cold or flu, respiratory tract congestion and voice not normal, fatigue and heart rate unstable was not reported. This report was serious (Hospitalization Caused / Prolonged).; Sender's Comments: V0:20210525842-Covid-19 vaccine ad26.cov2.s-Heart rate increased ,heart rate unstable. These events are considered unassessable. The events has a compatible/suggestive temporal relationship, is unlabeled, and has unknown scientific plausibility. There is no information on any other factors potentially associated with the events.