1) Epicycloid 1) Heart 
A cardioid (from the Greek καρδία `heart`) is a plane curve traced by a point on the perimeter of a circle that is rolling around a fixed circle of the same radius. It is therefore a type of limaçon and can also be defined as an epicycloid having a single cusp. It is also a type of sinusoidal spiral, and an inverse curve of the parabola w.....
heart-shaped
• (n.) An algebraic curve, so called from its resemblance to a heart.
A heart-shaped curve first studied in 1674 by the Danish astronomer Ole Römer who was trying to find the best shape for gear teeth. The curve appears to have been named by Giovanni Salvemini de Castillon (1708-1791). When a circle rolls around another circle of the same size, any point on the movi...
Resembling a heart. ... Origin: cardi-+ G. Eidos, resemblance ... (05 Mar 2000) ... 
A type of directional microphone that is more sensitive to sound from one direction, and rejects unwanted noise from the sides. (UK) 
Car'di·oid noun [ Greek 
Type: Term Pronunciation: kar′dē-oyd Definitions: 1. Resembling a heart.
[n] - an epicycloid in which the rolling circle equals the fixed circle
noun an epicycloid in which the rolling circle equals the fixed circle
Heart-shaped curve traced out by a point on the circumference of a circle, resulting from the circle rolling around the edge of another circle of the same diameter. The polar equation of the cardioid is of the form: r = a(1 + cos θ) where the...
Heart shaped pickup pattern characteristic of some microphones which reduces sensitivity to sounds f