Onyx stone is associated with the planet Mercury , which is known to represent intelligence, elevated brain power, and memory.   Onyx helps you stay focused on your goals and bring them to fruition.  Onyx opens and balanes the root and third eye chakra.   If you struggle with statying on task try working with onyx to help stabilize your energy helping you to keep moving forward.   
 
The crystal heart shape is used to show emotion or affection.  Love for self, love for others.  Carry a heart shape crystal for self care.  Give a heart shape stone to someone to show you are invested in their well being.