Robert Tools, who won the hearts of millions of Americans after becoming the recipient of the world's first totally implantable artificial heart, died Friday at Jewish Hospital in Louisville from uncontrolled abdominal bleeding and multiple organ failure.

Tools' death, and the death of a man receiving the 6th artificial heart during surgery earlier in the week in Houston, put a damper on the almost unbridled optimism that has surrounded the clinical trials of the AbioCor mechanical heart for the past five months.

When Tools received the implant July 2, doctors said they would be happy if he lived with the new heart for 60 days.

But Tools' recovery exceeded all expectations. Several months after the implant, he was making frequent trips outside the hospital, including lunches at area restaurants, fishing with his physicians and an evening at a comedy club.

"We will miss Bob's laugh, his sense of humor and his fighting spirit,'' said Dr. Rob D. Dowling, one of his surgeons. "Mr. Tools and his family members are heroes. Their willingness to be the first to participate in the AbioCor clinical trial could potentially pave the way for a revolutionary treatment option for advanced heart disease."

Only two days earlier, an unidentified man suffering from chronic heart failure became the first patient of the AbioCor trials to die during efforts to implant a mechanical heart at St. Luke's Episcopal Hospital in Houston. The surgical team spent 20 hours trying to control bleeding during surgery in the man.

Four other patients who have undergone AbioCor implants -- one in Louisville, one in Houston, one in Los Angeles and one in Philadelphia -- are still alive.