HeartWare International Inc. reached a milestone in the clinical trial of its left ventricular assist system, as the 50th U.S. subject was implanted with the device.

The Framingham, Mass.-based cardiac device maker said the trial is aimed at evaluating the system as a bridge to transplant for patients with end-stage heart failure, examining survival rates 180 days after implantation.

The system’s main feature is a miniature pump designed to assist the left ventricle in circulating blood, implanted next to the heart. The Food & Drug Administration granted an interventional device exemption for the clinical trial, which is targeting 150 patients at 28 centers (16 centers are enrolled).

HeartWare said it expects steady expansion in enrolled centers in the coming months.

The company has been busy lining its coffers lately, taking a loan and selling stock to help offset losses.

Onetime suitor Thoratec Corp. agreed to a $4 million loan, despite the companies spiking their merger after the Federal Trade Commission moved to block it on anti-trust grounds.

That loan and the $24 million HeartWare raised in a private stock placement will help shore up HeartWare’s $6.9 million net loss for the three months ended June 30, posted on about $3 million in sales.

Company officials said they expect the infusions to be sufficient to support its operations through the end of 2010.