It's nearly February, and cardioid shapes will appear on everything from food labels to flowerpots. Though the shape represents hearts, love and even the act of loving, it first and foremost is named for and represents THE human heart even though our hearts bear absolutely zero resemblance to the shape. The "heart" shape looks more like a V with rounded connectors, or two lobes getting pinched at the bottom. That shape is found more ON the human body than within it. "Cardioid" is even a class of microphone reception pattern (compare to omni).
So, why don't we give valentines with real hearts on them? Perhaps the same message would not be conveyed.