After Nora announces her intention to marry and settle down, Barney is worried; meanwhile, Robin's new boyfriend displays idiosyncrasies that remind her friends of a dog.
At dinner, Barney became worried when Nora began talking about marriage and settling down; he claims he wants the same things.
They see that Barney's heart literally skipped a beat, which he and Lily interpret as a sign he really wants to settle down.
He is nicknamed Scooby, and his behavior closely mimics a dog, which causes the gang to make a series of puns and jokes, to Robin's annoyance.
When Robin goes to work, Scooby and the rest of the gang consume marijuana (with Ted replacing it with sandwiches in his story to his kids).
The episode ends with a flashback of an incident involving Marshall in 2006, which explains the event Barney referenced when blackmailing him.
"A Change of Heart" first aired on February 28, 2011, garnering 9.24 million views on CBS and a 5.6/9 Nielsen rating.