Batman: Gotham Knights #73 (2006)

A news helicopter pilot, a corporate executive, and a train driver all drop dead of sudden heart attacks during routine moments of their respective jobs. Sam Roberts, the young medical examiner, determines that all three had exactly the same model of WayneTech pacemaker. Bruce Wayne soon faces intense media criticism for his long-standing lack of interest in his company. As Batman, he breaks into the GCPD to read Roberts's reports, and determines the mechanism by which the pacemakers were modified to induce the heart attacks. He decides the most likely suspect is the villain with knowledge of both medical matters and his secret identity: Hush. However, when he tracks down Hush (who is standing on a rooftop for some reason), Hush denies any knowledge of the deaths, though he does say he wishes he'd thought to do it. Batman eventually believes him, leaving the hero to wonder who else could be responsible. On a different rooftop, the Joker talks to a bird with an odd collar about how good it is to be back in Gotham, as well as his plans for revenge on both Batman and Hush. A henchman arrives and, after reporting on his progress, asks where he got the birds. The Joker recounts his experiences since his last encounter with them, being nursed back to health by two deformed people living in an abandoned carnival, then finding the birds after one died and the other fled. He trained the birds to do his bidding, and when a county tax assessor came to the carnival, he set them loose on the man, who had a heart attack as a result. The Joker attempted surgery, which was unsuccessful due to his lack of medical training, but gave him the idea for his current scheme. A brilliant surgeon gets off work and decides to unwind with a prostitute. They get a room, and the prostitute asks if it's okay if a friend joins them. The surgeon is receptive, but discovers that the "friend" is in fact the Joker.