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Exhibit 31.3

CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICER

Pursuant to Rule 13a-14(a) adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002

I, Catherine Szyman, certify that:

1.

I have reviewed this Amendment No. 1 to the Annual Report on Form 10-K of Masimo Corporation; and

2.

Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

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Dated: May 1, 2026

/s/ CATHERINE SZYMAN

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Catherine Szyman

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Chief Executive Officer

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(Principal Executive Officer)

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