Then how exactly you want to control it? Artificial heart won't speed up/slow down automatically in response to oxygen needs of your body because it is not controlled by nervous system
Controlling it with a smartphone isn't going to cut it either. How often, and how quickly, does your heart rate change by more than, say, 5%? Ten times an hour? More? Do you really want to be whipping out your smartphone every couple of minutes? What if you set it wrong? What if you fat-finger yourself into a blackout? What if the phone's battery is dead? The list goes on and on. It's a terrible user experience! Ask people who wear portable insulin pumps - devices that need input tens of times per day, and can be lethal if done wrong. (Some of them can be operated via smartphone these days, too.) They will tell you, emphatically, that they don't want to interact with that damn thing any more than is absolutely necessary.
No, you want the device to have its own closed loop mechanisms for controlling heart rate. The heart doesn't respond solely (or even primarily) to the nervous system. It responds to blood pO2, pCO2, and other chemical signatures in the blood. These characteristics, too, can be used as the feedback signals for the internal control system. The use case described in the summary - commanding it into certain pre-programmed profiles - is conceivable, but I don't think you necessarily want to rely on that.