My black lab went running today and came home very slowly and not putting any weight on his left back leg and he is whining/crying and just laying around. Any ideas on what it could be? Do I need to take hime to the Vet ER?

If you couldn't put any weight on one of your legs and spent all your time whining and crying would you go to the ER?

If so, take him.

He could have strained a muscle or stepped on something sharp. The only real way to tell is to look over his paws for any splinters, sores or swelling, if nothing is showing, he may need to go to the vet for an exam or x-rays.

Thanks for the sound medical advice... there is always one in the crowd.

Thanks I checked his paws and there was nothing,so I took him to the vet and he strained a muscle but will make a full recovery. He has done this before but never this bad.

I am so glad to hear he is going to be okay! My dogs have strained muscles and it's always nerve racking. Hopefully he can make a full recovery with no long term damage. Try to give him a few days rest, and did your vet okay to give Aspirin? It can help reduce any muscle swelling and relieve pain. Remember that any dog with a heart issue should not be taking any human versions of Aspirin. But, if not, as long as you follow proper dosing guide lines he should be okay. Of course your vet will know best, so make sure to run it by him first ;)