Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of health-care "payment management solutions" provider Emdeon (NYSE: EM) plunged as much as 10% this morning on the back of a downgrade to "market perform" from analyst William Blair.

So what: News that Blackstone (NYSE: BX) was interested in buying Emdeon for $3 billion drove up Emdeon's stock 22% in intraday trading yesterday. And rightly so -- if the rumors are correct, we're talking about a purchase price more than twice as high as Emdeon's current market cap.

Now what: But here's the problem: Emdeon's not worth $3 billion. Not even close. I mean, at $1.4 billion in market cap, the stock already costs nearly 65 times what it earned last year. Even if you value the company on its free cash flow, the $94 million Emdeon generated in "cash profit" over the past year prices this stock at more than 14 times FCF today.

Now, a multiple of 14 might be a fair price if Emdeon achieves the 14%-plus growth targets that Wall Street has laid out for it. But 28 times free cash flow? Seems a bit rich to me, and it seems William Blair agrees. My advice: If Blackstone is crazy enough to offer $3 billion for your Emdeon shares, take the money and run.

What will come of Blackstone's buyout offer? Add Emdeon to your watchlist and find out.

Fool contributor Rich Smith does not own (or short) shares of either stock named above. Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.