The S&P/ASX 200 Index (ASX: XJO) is having a very poor start to the week. In afternoon trade, the benchmark index is down 1.7% to 8,388.5 points.

Four ASX shares that are falling more than most today are listed below. Here's why they are sinking:

Fisher & Paykel Healthcare Corporation Ltd (ASX: FPH)

The Fisher & Paykel Healthcare share price is down 8% to $31.62. This has been driven by news that the medical device company expects to be impacted by US trade tariffs. For the first half of FY 2025, approximately 43% of revenue came from the United States. And approximately 60% of US volumes are supplied from the company's Mexico manufacturing facilities. These facilities will now be subject to 25% tariffs. Management believes the tariffs could mean it takes two to three years longer for it to achieve its gross margin improvement target.

Magellan Financial Group Ltd (ASX: MFG)

The Magellan share price is down a further 6% to $9.84. This means that the fund manager's shares have fallen approximately 20% since this time last week. The catalyst for this is news that Gerald Stack is exiting as Head of Investments after 18 years with the firm. Magellan notes that Stack has been Magellan's Head of Investments for more than a decade and over the past two years has contributed to important initiatives to strengthen the Investment Team. In response to the news, this morning, UBS has downgraded its shares to a sell rating with a $10.30 price target. UBS suspects that the exit could mean ratings agencies and consultants are likely to review their forecasts, raising the risk of outflows.

Resolute Mining Ltd (ASX: RSG)

The Resolute Mining share price is down 8% to 38.2 cents. This follows news that the gold miner's CEO, Terry Holohan is leaving his position with immediate effect. He will be replaced by Chris Eger, who has been acting CEO during Holohan's leave of absence. Resolute notes that Eger has been the CFO at Resolute since joining the company in February 2023. He has over 25 years of experience leading strategic, financial, and commercial functions of businesses in the natural resources and financial sectors.

Westgold Resources Ltd (ASX: WGX)

The Westgold share price is down 12% to $2.26. Investors have been selling this gold miner's shares after it downgraded its guidance for FY 2025. Westgold has lowered its production guidance range to 330,000 ounces to 350,000 ounces. This is down from its previous guidance of 400,000 ounces to 420,000 ounces. Its cost guidance has also been increased. Westgold's CEO, Wayne Bramwell, commented: "Optimisation of our expanded portfolio began in earnest in Q2 FY25 and disappointingly, engineering ramp up issues constrained outputs from the Beta Hunt and Bluebird-South Junction underground mines."