Heart - Your forehead is wider than your chin, your chin may come to a point. Choose frames that will help balance your face shape, and avoid frames that are top heavy, like semi-rimless (no frame on the bottom) or with a definite heavy pattern or colour on the top of the frame. Balance is the key here.
Oval - Considered the most balanced of the four face shapes, here you don't want to upset this natural balance. This face shape suits just about all frame styles.
Colour and style
Make sure the colour and style of the frame actually suit you. I know this sounds obvious, but don't choose a black frame if your overall colourings are better suited to warm colours like browns and greens.
Think about your personality, your style personality. If your personality is more expressive, confident and perhaps fashion-forward, choose a bold frame to match this. Glasses make a great fashion accessory.
Intended use
How practical are the glasses for what you need them for?
And how long would you like the glasses to last - this may affect the colour and style you choose, ensuring they don't quickly go out of date.
My advice is to seek help from the experts.
Get them to help you narrow down some options.
Ask to take a few pairs home so you can seek others' input, have a bit more time assessing each and also trying them on with the different clothes in your wardrobe.