An implantable system for stimulating a human heart or an animal heart, comprising a processor, a memory unit, a stimulation unit for stimulating a His bundle or another cardiac region of a human heart or an animal heart, a sensing unit for sensing an electrical signal of this heart, and a diagnostic unit for checking functional parameters of the implantable system, wherein the memory unit includes a computer-readable program, which prompts the processor to carry out the following steps when the program is being executed on the processor: a) detecting, by means of the diagnostic unit, whether at least one malfunction state of the implantable system is present; characterised by the following steps: b) checking whether an electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit; and c) switching an operating state of the implantable system into a safety mode when a malfunction state was detected, the safety mode being selected at least from a first safety mode and a second safety mode, wherein i) the first safety mode is selected when the checking carried out in step b) has shown that no electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the first safety mode resulting in a first safety operation of the implantable system, in which the implantable system does not meet any specific requirements for His bundle pacing; and ii) the second safety mode is selected when the checking carried out in step b) has shown that an electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the second safety mode resulting in a second safety operation of the implantable system in which the implantable system is able to meet specific requirements for His bundle pacing. wherein the memory unit includes a computer-readable program, which prompts the processor to carry out the following steps when the program is being executed on the processor: a) detecting, by means of the diagnostic unit, whether at least one malfunction state of the implantable system is present; a) detecting, by means of the diagnostic unit, whether at least one malfunction state of the implantable system is present; characterised by the following steps: b) checking whether an electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit; and c) switching an operating state of the implantable system into a safety mode when a malfunction state was detected, the safety mode being selected at least from a first safety mode and a second safety mode, wherein i) the first safety mode is selected when the checking carried out in step b) has shown that no electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the first safety mode resulting in a first safety operation of the implantable system, in which the implantable system does not meet any specific requirements for His bundle pacing; and ii) the second safety mode is selected when the checking carried out in step b) has shown that an electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the second safety mode resulting in a second safety operation of the implantable system in which the implantable system is able to meet specific requirements for His bundle pacing. b) checking whether an electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit; and c) switching an operating state of the implantable system into a safety mode when a malfunction state was detected, the safety mode being selected at least from a first safety mode and a second safety mode, wherein i) the first safety mode is selected when the checking carried out in step b) has shown that no electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the first safety mode resulting in a first safety operation of the implantable system, in which the implantable system does not meet any specific requirements for His bundle pacing; and ii) the second safety mode is selected when the checking carried out in step b) has shown that an electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the second safety mode resulting in a second safety operation of the implantable system in which the implantable system is able to meet specific requirements for His bundle pacing. i) the first safety mode is selected when the checking carried out in step b) has shown that no electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the first safety mode resulting in a first safety operation of the implantable system, in which the implantable system does not meet any specific requirements for His bundle pacing; and ii) the second safety mode is selected when the checking carried out in step b) has shown that an electrode provided for stimulating a His bundle of a human heart or an animal heart is connected to the stimulation unit, the second safety mode resulting in a second safety operation of the implantable system in which the implantable system is able to meet specific requirements for His bundle pacing.