Draw the outline of a heart with a light color. If using colored paper, start with a color that does not stand out much. This initial outline will serve as a basic scaffold on which to add color, dimension and emotion. Draw lightly and freely as if you are shaping the heart in clay until it is close to the shape and size you want. Don't draw a hard, rigid outline as the rest of your drawing will be bound by it.
Using lighter colors first, redraw your outline and add color to your heart. One of the virtues of pastels is that they can be smudged and blended, so experiment by using your fingers and pushing the colors around. With your fingers, blend the pastels along the contours of the heart.
Draw darker colors over the lighter colors. The darker colors can bring out the three-dimensionality of your heart when you add shadows to the curves. Shadows do not have to be black or grey; they can be any darker shade of a color already used. Darker colors can add textural contrast if you choose not to smudge them. The finer edges of the dark colors can contrast with the smoother smudged surfaces of the light colors.
Draw details and background. If you want your heart drawing to be playful and exuberant, add shapes on the heart and textures like contour lines to make it stand out. If you want it to be more sculptural and elegant, consider keeping the drawing simple and focusing on precise shadows and shading. The color and texture of the background will influence the look of your composition.