Season 6: Episode 18 - A Change of Heart

A Change of Heart: After the death of Marshall's father, the gang decides to all get their hearts checked out by a doctor. Barney has a slight irregularity and must wear a heart monitor on his date with Nora. Through the doctor's analysis of his EKG, we learn that Barney has true feelings for this girl but is too afraid of a serious relationship. Meanwhile, Robin starts dating a guy "Scooby" who ironically acts just like a dog.