Kathy Goolsby/ Dallas Morning News

James Hamilton's heart fills with love as he watches his 11-month-old son Bowen, toddle around the coffee table in the family's Hurst apartment. It's a feeling the 26-year-old first-time father once thought he'd never experience, in part because the heart that beats inside him once belonged to someone else.

"There's a certain percentage of male transplant patients who end up sterile because of the medications," said Mr. Hamilton.

He was three months shy of his 19th birthday when he suffered chronic fatigue and respiratory problems. Mr. Hamilton thought he had the flu or pneumonia, but the doctor sent him to the hospital for tests. He was diagnosed as having endocarditis, which had destroyed the inner lining of his heart.

It was the same virus that killed his mother, Cathy Hamilton, nine years earlier at age 29.

"It was odd, but on the ride to the hospital I knew somehow I had the same thing as my mother," he said. "In a way, it made me more determined to beat it. My mother and I were very close, so I felt like I was doing it for both of us."

Mr. Hamilton was in and out of the hospital over the next nine months. Finally doctors implanted a left ventricle assist device (LVAD) to help his heart pump while he waited for a donor.

Being on the device required full-time hospitalization, and during the yearlong wait, Mr. Hamilton had plenty of time to think about his future.

Even if he didn't become sterile, he wondered what effect the medicines might have on his children.

"It's a particular concern with women since they carry the baby, but in men there's the question of it interfering with the development of healthy sperm," said Dr. Marlon Levy, medical director for the Southwest Transplant Alliance. "Unfortunately, our data is not as complete as we would like, but for the men taking these drugs there seems to be no difference between their children and others."

But Mr. Hamilton, who was 20 when he had the transplant, also was concerned about how long he would live.

"I was thinking, 'Wow, heart transplant patients have a 20-year life expectancy. How can I get married, have children and then leave them?' " he said. "I've seen what my mother's death did to my dad, so I swore off women."

But that didn't keep him from talking with the opposite sex in Internet chat rooms. That's where he struck up a friendship with Melissa Murdock, a high school senior in Idaho.

The two discovered they had a lot in common, including the deaths of their mothers at an early age. Within a year of his transplant, Mr. Hamilton drove to Idaho to meet Ms. Murdock, and their friendship deepened into love.

Mr. Hamilton's heart problems at first made them both leery of marriage.

"I had some real heartbreak thinking about that, but then I had a talk with my dad," his wife said. "He said, 'He could walk out the door and get hit by a car tomorrow. But if you love someone, you don't think about that. You love for today.' "

They married Sept. 21, 2002, in Fort Worth. It was his wife who convinced Mr. Hamilton they should have children by pointing out medical advances that have been made since his mother died.

"The LVAD they put in me would have kept her alive, but they didn't have it then," he said. "Who knows what they'll come up with in the next 10 years?"

The Hamiltons both worked in bill collections, but Mr. Hamilton was fired for taking a day off to be at his son's birth on July 15. He became a stay-at-home dad, which allowed him to finish writing a science fantasy novel he's pitching to publishers.

He recently started a loan-processing job with an insurance company. He'll miss taking care of Bowen every day, but he's grateful for the close relationship they've developed.

"He's always reading Dr. Spock, trying to be the best dad," Mrs. Hamilton said. "Not every dad has the opportunity to be home with their kids when they're little."

As he watched Bowen work his way around the table and listened to the boy's bubbly laughter, Mr. Hamilton said he had no big plans for his first Father's Day. The family plans go to church and the zoo, then spend time with Mr. Hamilton's dad, Jimmy Hamilton of Springtown.

Mostly, he's just enjoying being a dad.

"I'm glad Melissa talked me into having children," he said. "Like every new dad, I was delighted and scared when Bowen was born. I know I can take care of myself, but now I need to watch out for him too."