Heart development begins with the induction of cardiogenic cells from the embryonic mesoderm, followed by the coalescing of these cells into a linear heart tube. Subsequent looping of the heart tube brings the rudimentary atria and ventricles into alignment for further development into the four-chambered heart. Underlying these morphologic events is a complex program of signaling between cells and tissues that orchestrates their participation in heart development. Among these signals are bone morphogenetic proteins, fibroblast growth factors, Wnts, Hedgehog, and members of the transforming growth factor-beta family of signaling molecules. We review here the various properties of these signaling molecules and their signal transduction pathways in hopes of providing a greater appreciation of the molecular events driving heart development.