Billy McKay scored twice and missed a penalty after Hearts skipper Jamie Hamill was sent off for handball.
Locke said: I spoke to Jamie Hamill after the game and he said the ball hit him on the head, but when I spoke to the referee, he said it was handball.
"It's a difficult one, but I don't really want to make too much of it as I don't want to make any excuses.
"Inverness were really good and twice caught us in the first half on the counter attack.
"You are going to get these days. We've had a great few weeks where we've not really had many setbacks, so it's not the end of the world."