The stock market kept climbing on Monday, with modest gains across major benchmarks that nevertheless sent the Dow Jones Industrial Average to its ninth straight record high. Absent major news in the August summer doldrums, investors largely focused on earnings reports and merger announcements, and conditions appear to remain favorable even as Wall Street heads into a historically volatile season. NxStage Medical (NASDAQ:NXTM), MyoKardia (NASDAQ:MYOK), and Rockwell Collins (NYSE:COL) were among the best performers on the day. Below, we'll look more closely at these stocks to tell you why they did so well.

NxStage gets an offer it can't refuse

Shares of NxStage Medical soared 28% after the maker of home dialysis equipment received a buyout bid from Fresenius Medical Care (NYSE:FMS). Under the terms of the deal, Fresenius will pay NxStage shareholders $30 per share in cash, putting the total value of the acquisition at about $2 billion. Fresenius CEO Rice Powell said that the deal will "support our 2020 strategic initiative of driving growth in the core business," while NxStage CEO Jeff Burbank pointed to "the potential to significantly advance the standard of care for patients around the world." With the deal expected to close next year, both companies will still have time to keep moving forward in their respective businesses before joining forces.

Person sitting on a chair next to a home dialysis machine.

Image source: NxStage Medical.

MyoKardia looks a lot healthier

MyoKardia stock skyrocketed more than 80% in the wake of news that the heart-ailment biotechnology specialist had seen good results for its lead drug candidate mavacamten. The company said that the phase 2 study of the drug formerly known as MYK-461 had met the primary endpoint of favorable changes in post-exercise peak left ventricular outflow tract gradient over the 12-week course of the study, and had also met key secondary endpoints such as peak VO2 levels of oxygen consumption. Safety data was also favorable, and MyoKardia chief medical officer Marc Semigran said that the results "further demonstrate the potential of mavacamten in [obstructive hypertrophic cardiomyopathy] and we intend to move decisively and with urgency to develop this potential therapy for patients." Investors can expect that MyoKardia will push for a phase 3 trial with the eventual goal of applying for approval of the drug.

Will Rockwell get a big buyout bid?

Finally, Rockwell Collins stock climbed 7%. Shares of the avionics specialist jumped in response to reports that United Technologies (NYSE:RTX) might be interested in buying the company, with some speculating that United Tech adding the complementary business to the rest of its aerospace exposure would make some sense. Critics believe that the timing is far from ideal, especially because some primary aircraft manufacturers are making moves toward vertically integrating avionics production of their own. For those investors who might be nervous about the big move that Rockwell made to buy B/E Aerospace last year, a buyout might be the perfect exit strategy.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.