o create the texture use the Rectangle Tool, draw a very small square. Duplicate it and place it next to the first one then press the right arrow key on your keyboard to move it a bit to the right. My keyboard increment is set to 1 px so I pressed 2 times to move it away from the other one. Select now the 2 squares, multiply them and do the same to move them, then when you have 4 squares multiply them all at once to finish the first row faster. Multiply this row until the texture is big enough to cover the heart shape. Group all the squares, rotate them a bit to the right to fit with the position of the heart, place them on top, select both the texture group and the smaller heart shape made earlier (that must be on top) and go to Object > Clipping Mask > Make.