Dr. Louie Darnell, a cardiac specialist, was first introduced as the replacement for Dr. Justin Marler when Justin left Springfield with his infant daughter Samantha Marler and Helena Mancini. Upon arriving at Cedars, Louie saw a familiar face—Dr. Claire Ramsey. Louie and Claire had apparently known each other in college. The pair had dated, and while, Louie wanted something more, Claire did not.

Louie's first big case occurred when businessman Henry Chamberlain was admitted to Cedars after suffering from a heart attack. Though Henry almost died when he was given the wrong dosage of his medication—something that Nurse Lesley Ann Monroe was accused of doing. Luckily for Lesley Ann, Louie was able to clear her name when Louie noticed that someone had changed the dosage that Louie originally prescribed on the chart. Soon after, someone tried to disconnect Henry's life support but, luckily, Louie and Rick Bauer discovered Henry and saved him. Cedars head nurse Lillian Raines was accused of disconnecting Henry's life support, but Louie was able to clear Lillian's name when he found that there was a discrepancy in the time that Lillian was in Henry's room and the time that the life support had been disconnected. Finally, in November 1983, it discovered that criminal Eli Sims) had disconnected the life support and changed the dosage on Henry's chart. After Eli's arrest, Henry made a full recovery.

Meanwhile, Louie moved into the garage apartment at the Bauer house. There, Louie became good friends with his roommate, Rick Bauer. Louie listened "on and on" to Rick complaining about still being a virgin. After several months, Louie, still unhappy that Claire had turned him down, bet Rick that he couldn't lose his virginity to the frigid Claire. Rick took the bet and later, to Louie's shock, won it.

After a failed relationship with Katie Parker, Louie began dating Maeve Stoddard. Unfortunately, Maeve got distracted by Kyle Sampson who was having a hard time dealing with Reva Shayne Lewis. Kyle and Maeve ended up having an affair and when Maeve ended up pregnant, she and Kyle got married.

In the spring of 1986, after briefly dating Billy Lewis's office assistant, Wanda M. Hite, and realizing they didn't have much in common except for being two lonely hearts, Louie settled for being the best cardiac specialist he could. Louie also helped his friend Rick recover from his drug addiction and pass his medical exams so he could get his medical license. After Rick conquered his drug addiction with an intensive rehab program -- Claire ended up being the doctor who administered Rick's medical exams and ultimately failed him.

Meanwhile, Maeve kept noticing how much time Kyle spent with Reva and started to become jealous. Maeve soon left town and gave birth to a baby boy. Unwilling to live with a man who didn't love her, Maeve told Kyle Kyle that their child had been stillborn and that she wanted a divorce. Reva and Kyle soon became engaged, not knowing that Maeve had secretly given birth to a son named Ben. Maeve pulled Louie into her lie by getting him to agree to pass off Ben as his orphaned cousin. Although, Kyle and Reva bought the story that Ben was his orphaned cousin -- Claire quickly pieced together what was really going on. By this time, Louie had figured out that Claire vindictively gave Rick a failing grade. When he confronted her, Claire blackmailed Louie to keep silent by threatening to reveal what she knew about Ben. Finally, Maeve crashed Kyle and Reva's wedding ceremony and revealed that Ben was her natural son by Kyle. By this time it was December 1986, and Louie, having had enough of being used as nothing more than a pawn in the games of both Maeve and Claire, decided to resign from Cedars and left for parts unknown.