I believe what you want is the paint brush. After picking the color, you can simply brush over the text.
Or, more precisely you could use the rectangular fill with it set to fill shape.
Just go over the text without disturbing too much of the image.
After you create you new layer, select it. Then go to the layers drop menu and select import from file.
Choose the heart picture. It will appear on the layer, but it will ask you if you want to resize the canvas.
Choose expand as this will allow you to see the whole heart image. Delete the white and feather the hearts.
From here you can use the magic wand to select a blank space and invert your selection(Ctrl+I).
You can use the move pixels tool to quickly resize the hearts. Hold shift as you grab a corner and drag it in.
When it's smaller you can crop your image down.
If you have the second layer selected when you are finished, then you will see the merge down button in color.
And you should have something like this:
You can see the area on the left where I replaced the text slightly, but when you do it try to blend your changes more into the pattern the image already has.
Depending on the placement/size of your text you can have a bit of leeway.