yorkie in heat

Question
how long does it usually last when she is in heat and there has been no sign of bleeding  i have a male maltese going crazy all over her? also CAN A MALE DOG OF 8LBS BREED WITH A 4LBS YORKIE FEMALE?

Answer
lon,
you are taking a chance when you breed the larger male to a smaller female.  You might wind up with a c-section or a dead female.  This is not true of large breed dogs, but is definitely true of the smaller ones.   If your female is not bleeding or bleeding very little, there are two possibilities.
One is that she is very clean and you don't see blood, in that case it would last for about 3=4 weeks depending on individual tendencies.
Two she may have an infection and is giving off a blood scent; have her checked by a vet.
nancy