MILAN (Reuters) - Sorin, Italy's biggest listed biomedical group, has invested $8 million in U.S. medical technology manufacturer Cardiosolutions with an option to acquire the business in the future.

The agreement includes a plan to develop products and test Cardiosolutions' technology, a deal that adds to Sorin's investment in the United States after it announced a $14 million acquisition of California medical laboratories on July 2.

"The investment in Cardiosolutions confirms Sorin's commitment to continuously introduce innovation in the two areas we have prioritized, heart valves therapies and heart failure, and it represents an important step forward in our long-term growth initiatives," Sorin chief executive André-Michel Ballester said .

Massachusetts-based Cardiosolutions, set up in 2006, makes medical devices to help treat heart conditions using less intrusive operations.

Sorin, which has a market capitalization of 811 million euros ($997 million), has performed well as a defensive stock against a dire economic backdrop spurred by a chronic euro zone debt crisis.

Since the financial crisis took hold of major western economies in late 2007, Italy's main share index has shed almost 70 percent.

In June Sorin's two main shareholders said UK's Charterhouse was interested in buying a significant stake in the biomedical company but no formal offer had been made.

Sorin will announce its half year earnings on July 30.

(Reporting by Philip Baillie; Editing by David Cowell)