Heart Bar Frog Support Series. In each shoe, the heart bar supports or stabilizes P3 through the frog. As a general rule, the point of the bar should be 1/4" to 1/3" behind the apex of the frog and in full but gentle contact with it. Frogs should be soft and pliable. Compression should not exceed 1/8" of the frog. These shoes should be applied with x-rays and the consent of a veterinarian.