The most obvious sign you can look for that your pup is in heat is the swelling of her vulva. This is caused by an increase in blood flow to the area and will make her genitalia look larger than normal.
Another sign that your puppy is in heat is she will lick her genital area more excessively than usual.
The third sign of a puppy in heat is bleeding from her vulva. It is generally a straw-like color and can be a little inconvenient (especially if your dogs are allowed on the furniture).
You may find that your pup is more open to male company when she is on heat. This happens to even the most unfriendly of dogs.
You may notice that your pup is a little more nervous or agitated than usual when she’s in heat. This is likely because of all the changes her body is going through, and she may not know how to deal with them.