Tracy has spent the last two years changing diapers, bathing and feeding her son and enjoying the moments of a baby's progress-the first smile, crawl and step. 

Being a first-time parent is a thrill for most couples, but for Tracy, the experience is beyond anything she could have dreamed. Diagnosed with an enlarged heart, she had been incapable of walking even 10 feet. Then, at age 29, Tracy received a heart transplant. 

Not three months later, she got news she never thought possible: she was pregnant. Today, if Tracy is tired, it's from running after son Trent.