American Funds holds a 12.4% stake in Heinz, more than twice the 5.5% stake of dissident, billionaire shareholder Nelson Peltz of Trian Partners. And that means that American Funds could hold the key to whether Peltz, a self-proclaimed "operational shareholder activist," gets the three seats on the Heinz board he is seeking.

But one wrinkle is that American Funds doesn't necessarily vote all its shares as one block. Rather, the company encourages individual portfolio managers to vote as they see most fit for their shareholders, and at least six funds hold shares in Heinz. "You could have one [fund] that would vote one way and one that would vote another," said Chuck Freadhoff, a spokesman for American Funds.

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