The Roommate Transmogrification - S4-E24
Corrected entry: Bernadette tells Howard that she chose the premature ejaculation project because neither of them has any heart diseases. However Howard has stated more than once that he has transient idiopathic arrhythmia. Also in the previous episode he actually emphasizes that his family has a history of heart diseases and alludes to a cave painting showing one of his ancestors clutching their chest.
Correction: Transient idiopathic arrhythmia is not a disease, it is a disorder. They are different things.