Comments by a Federal Reserve official that tapering could begin in October sent the markets tumbling during the midday with the Dow plunging 100 points to 15,536. Nasdaq slipped 6 points to 3783.

On the upside

Shares of Sarepta (Nasdaq: SRPT) soared after a competing Duchenne Muscular Dystrophy treatment failed a study.

The stock price of FireEye (Nasdaq: FEYE) nearly doubled in its market debut.

Chardan Capital Markets analyst Jay Srivatsa lifted his price target on Himax Technologies (Nasdaq: HIMX).

On the downside

Profit taking sank shares of Frontline (NYSE: FRO).

Goldman Sachs initiated coverage of IAMGOLD (NYSE: IAG) with a Sell rating.

Motley Fool wrote that Zillow (NYSE: Z) was a bubble stock that would soon burst.  

In the broad market, declining issues outpaced advancers by a margin of more than 2 to 1 on the NYSE while advancers barely edged out decliners by a slim margin on Nasdaq. The broader S&P 500 fell 8 points to 1713.