The lower rating comes after Medtronic (MDT) agreed earlier this week to acquire the Framingham, MA-based medical device company for about $1.1 billion, or $58 per share.
Since the offer was announced, HeartWare stock has been trading within 50 cents of the bid and above Barclays' price target of $35.
"Given the run-up, we view HTWR as close to fair value; our prior upside target was $45," the firm wrote in an analyst note.
"While we acknowledge HTWR may be worth more to an acquirer given the potential for synergies, accelerated growth driven by a bigger combined sales force, and there could be upside from a successful deal, we think the current stock valuation implied by the market warrants a downgrade," Barclays added.
The firm also upped its price target on HeartWare stock to $58 from $35.
Shares of HeartWare closed at $57.55 on Tuesday.
Separately, TheStreet Ratings Team has a "Sell" rating with a score of D on the stock.
The company's weaknesses can be seen in multiple areas, such as its deteriorating net income, disappointing return on equity, weak operating cash flow, generally high debt management risk and generally disappointing historical performance in the stock itself.
Recently, TheStreet Ratings objectively rated this stock according to its "risk-adjusted" total return prospect over a 12-month investment horizon. Not based on the news in any given day, the rating may differ from Jim Cramer's view or that of this articles's author.
You can view the full analysis from the report here: HTWR