If you draw 10 in the goldfish pond, you are guaranteed to receive a hero, but if you draw coins in the Lilies Pond, you aren't guaranted to get a hero.  

There is a chance that you already have the hero that you receive. 

If you withdraw a hero which you have already summoned, you will get the hero’s soulstones instead and they are quite useful for powering up your hero by evolving it. 

Here are rules of how many soulstones you would get:

1 Star hero ->7 Soulstones

2 Star hero ->14 Soulstones

3 Star hero ->30 Soulstones

You can also get new heroes from collecting soulstones and equipment. How quickly you get a hero and which hero you get first largely depends on luck.