Mercedes sensed when my dad's heart would beat irregularly, when he fell off a ladder in the backyard, she laid across him and barked until the neighbours called 911. When the paramedics came to get my dad, they had to LIFT Mercedes off of him, she wouldn't leave him. She also learned to put her head on his lap when he was having a bout of irregular heart beats. This prevented him from falling when he was having an episode. He eventually got a defibrillator implanted, but she stuck pretty close to him when they were out and about.