Diarrhea and irregular heartbeat are the symptoms shown by the dogs when they eat something toxic or unsuitable for them. Examples of unsuitable foods are beer, wine, chocolate, coffee, tea, or some types of mushroom. The main reason behind irregular heartbeat is caffeine. Daffodils are the garden plants that can also cause the same problems if the dog eats them up. You just try to watch him closely and strictly restrict him to his normal diet. He will recover soon.