My doctor just suggested to me to take quercetin for my allergies and sinusitis. While I researched it online I came across a study suggesting quercetin can help with afib. Any thoughts? And is quercetin safe to take?

Yes, safe to take. You'll need a good form of quercetin like phytosome.

Quercetin improves atrial fibrillation through inhibiting TGF-β/Smads pathway via promoting MiR-135b expression

Results: The expression of miR-135b was downregulated, and those of TGFBR1, TGFBR2, target genes of miR-135b were upregulated in human AF tissues and negatively regulated by miR-135b in RCFs. Through inhibiting TGF-β/Smads pathway via promoting miR-135b expression, quercetin treatment inhibited proliferation, myofibroblast differentiation and collagen deposition in ISO-treated RCFs, as evidenced by reduced expressions of cyclin D1, α-SMA, collagen-related genes and proteins, and alleviated fibrosis and collagen deposition of atrial tissues in ISO-treated rats.

Conclusion: Quercetin may alleviate AF by inhibiting fibrosis of atrial tissues through inhibiting TGF-β/Smads pathway via promoting miR-135b expression.

[pubmed.ncbi.nlm.nih.gov]

Numerous more studies here [pubmed.ncbi.nlm.nih.gov]