Dave, Thank you for your question. I am a patient like you, and I had an allergic reaction to the Pfizer vaccine which was probably a reaction to the polyethylene glycol which is it. After that, I spoke with my allergist, and the vaccine that he was choosing for himself was the Johnson & Johnson. He told me it has a lot less side effects than either of the m-rna vaccines (which are the Pfizer and Moderna). Here is a link to information from the CDC about myocarditis and pericarditis (heart related) and the 3 vaccines that are available in the US. This information states:
"Since April 2021, increased cases of myocarditis and pericarditis have been reported in the United States after mRNA COVID-19 vaccination (Pfizer-BioNTech and Moderna), particularly in adolescents and young adults. There has not been a similar reporting pattern observed after receipt of the Janssen COVID-19 Vaccine (Johnson & Johnson)."

Here is the link: https://www.cdc.gov/vaccines/covid-19/clinical-considerations/myocarditis.html

Symptoms after vaccinations are reported and collected which allows researchers to look for links. Something that happens may not be related to a vaccine, or it may, but it will take some time to figure out. Some people have pre-existing conditions and already have inflammation which could be heart related in someone who is already developing heart disease.

This link explains how data is evaluated by VAERS, the vaccine Adverse Event Reporting System. One of the misconceptions of looking at the data is to assume that a vaccine caused a specific problem. "Generally, VAERS data cannot be used to determine if a vaccine caused an adverse event. VAERS data interpreted alone or out of context can lead to erroneous conclusions about cause and effect as well as the risk of adverse events occurring following vaccination."

Here is the link about safety monitoring. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4632204/

Does this help ease your mind? Have you discussed your concerns with your doctor?