3D printing is now being used as an aid to cardiac surgery. The printers don't yet make actual replacement hearts. What they do is use information from ultrasound images to construct three-dimensional duplicates of patients' hearts for surgeons to practice on:3D Print Heart Models
Here's an article about a baby in Baltimore, with a severe congenital heart defect, who's getting prepared for surgery through this method:3D Heart Model for Toddler
This technique does, however, have the capacity to produce simpler cardiac replacement parts, in the form of 3D-printed silicone heart valves:3D Print Heart Valves
A vital problem in growing artificial organs for transplant consists of providing them with a viable blood supply once they're implanted in the body. Creating "intricate networks of tiny blood vessels" is a major challenge. Now scientists at Rice University in Texas have made progress with "a 3D bioprinter that can print vessels less than a third of a millimeter wide in biocompatible hydrogels." They've even built an artificial lung capable of oxygenating blood:Biggest Challenge with 3D-Printed Organs
Here's a Smithsonian article about the prospects for lab-grown and 3D-printed organs:Printed Organs on Demand
Two obvious advantages of producing custom-made body parts on demand, of course, would be bypassing the donor shortage and avoiding any risk of rejection. Maybe in the future most of us will be cyborgs. Moreover, if such personalized replacements eventually become available to everybody, might we reach a point where people never have to die until they reach the upper limit of old age? Maybe our descendants in the near future will see the fulfillment of the biblical prophecy (paraphrased), "As the age of a tree shall the lives of my people be."
Margaret L. CarterCarter's Crypt