Fiserv's stock plummeted 44% Wednesday and headed for its worst day ever after the fintech company cut its earnings outlook and shook up some of its leadership team.

"Our current performance is not where we want it to be nor where our stakeholders expect it to be," wrote CEO Mike Lyons in a release.

For the full year, Fiserv now expects adjusted earnings of $8.50 to $8.60 a share for the year, down from a previous forecast of $10.15 and $10.30. Revenues are expected to grow 3.5% to 4%, versus a prior estimate of 10%.

During an earnings call Wednesday, Lyons said Argentina's deteriorating economic environment contributed to slowing growth and margin disappointment. Last year, the South American country contributed 10 percentage points to its 16% organic growth rate, he said.

Fiserv's original growth estimate "assumed that to compensate for the slowdown, our non-Argentinian businesses would grow significantly faster than their historical mid-single-digit range," he said.

Adjusted earnings came in at $2.04 per share, falling short of the LSEG estimate of $2.64. Revenues rose about 1% from a year ago to $4.92 billion, missing the $5.36 billion forecast. Net income grew to $792 million from $564 million in the year-ago period.

Along with the results, Fiserv announced a slew of executive and board changes.

Beginning in December, operating chief Takis Georgakopoulos will serve as co-president with Dhivya Suryadevara, recent CEO of Optum Financial Services and Optum Insight at UnitedHealth Group. Fiserv also promoted Paul Todd to finance chief.

"We also have opportunities in front of us to improve our results and execution, and I am confident that these are the right leaders to help guide Fiserv to long-term success," Lyons wrote in a separate release.

Fiserv also announced that Gordon Nixon, Céline Dufétel and Gary Shedlin would join its board at the beginning of 2026, with Nixon serving as independent chairman of the board. Shedlin is slated to lead the audit committee.

The Milwaukee, Wisconsin-based company also announced an action plan that Lyons said would better situate the company to "drive sustainable, high-quality growth" and reach its "full potential."

Fiserv said it will move its stock from the NYSE to the Nasdaq next month, where it will trade under the ticker symbol "FISV."

Fiserv did not immediately respond to CNBC's request for comment.