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Dealmaking has gone gangbusters in 2021.

Global mergers and acquisitions for the year just broke all of 2020’s full-year levels. By October, total dealmaking activity amounted to $4.4 trillion during the first nine months of 2021. That’s “an increase of 92% compared to year-ago levels and the strongest opening period for mergers [and] acquisitions since records began in 1980,” according to a recently released deals intelligence report from Refinitiv, a market data provider.

This year’s figures have already beaten 2015’s full-year record of $4.3 trillion, per Refinitiv. (You can see a decade’s worth of M&A data compiled in Refinitiv’s chart below.)

The environment has been ripe for the M&A boom, according to Marc Cooper, chief executive of Solomon Partners, a boutique investment bank (formerly known as PJ Solomon). Cooper points to pent-up demand in the M&A space coming out of the pandemic, low interest rates, and an “aggressively” growing economy fueling companies’ performance. There’s been a “long-term perspective that we’re going to have easy money out there” and ample government spending, he told Fortune.

But if there’s one thing that has the potential to cool the dealmaking frenzy, it’s changes to Federal Reserve policy that could set rates on an upward path. “Interest rates are really the top on the hit parade,” Cooper argued.

“As rates go up, I think it will have a dampening effect,” he said. While businesses could still “easily” do transactions if interest rates tick higher, “the question will be how it affects the stock market” given the tie between market performance and M&A, Cooper suggested.

“If interest rates go up enough and if people have the view that the economy is going to be throttled back, yes, you could see a downturn in the stock market which would have a negative effect on the M&A market,” Cooper said.

Since higher bond yields could start to appear more attractive compared with other assets, investors could shift more into fixed-income securities and back off from equities, Cooper noted. “It also means financing costs are higher, so lower returns,” he said.

When any of this might take place, though, is still up in the air. Last month the Federal Reserve signaled it may begin tapering its asset purchases before the end of 2021, and there’s the possibility a rate hike could come in 2022 or 2023, according to Fed members. Lately, investors have seemed more concerned about higher inflation sticking around, as bond yields have been rising amid a rough patch for stocks in recent weeks.

To be sure, the M&A market doesn’t appear to be running out of gas just yet. There are dealmakers who argue the activity can continue, perhaps at an even higher rate, from here.

Other market-watchers, like Matt Toole, director of deals intelligence at Refinitiv, note that it’s hard to make predictions. “With the all-time full-year dealmaking record broken in less than nine months and five consecutive quarters of more than $1 trillion in M&A activity, we have very little data to make true historical comparisons,” Toole wrote in a note alongside Refinitiv’s deals report.

That said, “we do know all of the hallmarks of previous cycles—technology M&A, private equity—are driving towards new records,” Toole noted. “Coupled with a group of new SPAC buyers and incredibly friendly credit markets and strong stock prices, all ingredients for robust M&A will continue for some time,” he forecasted.

But even now, Solomon Partners’ Cooper points to another complication running counter to companies’ merger prospects: antitrust activity. The regulatory environment “is definitely having an effect on strategic mergers, and everyone’s scared as hell,” Cooper said. That “doesn’t affect the private equity community,” he noted, “but when it comes to strategic buyers, it’s a major issue.”

Indeed, there could be headwinds brewing. “A more active regulatory environment in the U.S., rising inflation, global economic and diplomatic tensions, and easing central bank intervention will all contribute to how much further this cycle has to go,” Refinitiv’s Toole said.

“Dealmakers are watching closely,” he added.