Using a pram is actually a great way to get a dog to heel!
It is very important that your dog knows what heel is.
Make sure you teach the heel position in a quiet boring location - usually indoors to start with.
Do you have a long hallway or kitchen.
Put the dog between you and the wall (I would use a clicker and treats)
Lure the dog into the correct position with the treat and then walk one step give the dog the treat as you are moving.
Because you are close to the wall the dog will have less places to wonder off to.
DO NOT use the heel word here at all. - the dog is learning the behaviour first - then add the word.
if you have been saying heel, then change to a new word when you are ready eg close, side or with me.
When your dog is good at this indoors put on a lead and do it again in the hallway - make sure that you are not in anyway letting the lead go tight - if you do you are teaching the dog to pull against you.
If the dog does go forward just stop and lure back into the correct position and carry on again treat after a few forward steps.
Do this for a while.
To see if the dog has learnt the heel position stand next to the dog and step to the side and then ask heel - the dog should also step to the side to the hell position.
You are not ready to take this on location!
Try in your garden first if possible again against a wall, try dow the pavement again next to a wall. IF the dog does go in front stop. pause, quietly say the dogs name and lure back into the hell position continue on for a few steps and then reward.
This will take time - and do not expect the dog to be perfect or to heel in all situations to start with eg when out walking on the common and their is another dog , or a pheasant to chase! So build it up and do not expect too much too soon. Most dogs will need constant training in heel work, especially if they have learnt to pull.
Your pram will actually be a positive aid - if the dog does pull ahead you can block with the pram and the wall so will clearly show the dog the correct position.
Let us know how you get on. But remember in dog training if you want a good result quickly go slowly!