When a female dog is in heat, an intact and sexually mature male dog in the area can act anxious and aggressive towards other male dogs. He loses interest in anything except mating. A neutered male dog usually acts normally around a female dog in heat.
Urine marking is a common behavior exhibited by a male dog in the presence of a female dog in heat. He marks because of his level of excitement and to gain attention from the female. Female dogs in heat also urine mark, and the hormones in the urine attract male dogs. A male dog may break out of his backyard if he smells the female dog's urine, as the scent can carry up to a mile.
Male dogs are aggressive towards one another when a female is in heat because they are competing for her affection. They both want to mate with her and may fight over her.
Since neutering a male dog involves the removal of his sex organs and the hormones they produce, he doesn't act differently around a female in heat. It can take between 6 and 8 weeks for the hormones to leave his body. A male dog that is neutered at an old age may retain his old behavior.