An implantable medical system configured to coordinate ventricular pacing with intrinsic depolarizations of another chamber of a heart of a patient, the system comprising: a leadless pacing system comprising: a leadless pacing device comprising: a stimulation module configured to generate pacing pulses; a sensing module; a processing module; a housing configured to be implanted on or within a ventricle of the heart, wherein the housing encloses the stimulation module, the sensing module, and the processing module; and a first electrode electrically coupled to the sensing module and the stimulation module; and a sensing extension extending from the housing and comprising: a body extending from the housing; and a second electrode carried by the body and electrically connected to the sensing module and the stimulation module, wherein the sensing module is configured to sense electrical activity of the ventricle via the first and second electrodes, and the stimulation module is configured to deliver pacing pulses to the ventricle via at least the first electrode; and another implantable medical device configured to: sense an intrinsic depolarization of the other chamber of the heart of the patient, and in response to the intrinsic depolarization of the other chamber, deliver an electrical pulse, and characterized in that the sensing module of the leadless pacing device is configured to detect the electrical pulse delivered by the other implantable medical device via the first electrode and the second electrode, and, in response to the sensing module of the leadless pacing device detecting the electrical pulse delivered by the other implantable medical device, the processing module of the leadless pacing device is configured to control the stimulation module of the leadless pacing device to generate a pacing pulse for delivery to the ventricle via at least the first electrode in coordination with the intrinsic depolarization of the other chamber. a stimulation module configured to generate pacing pulses; a sensing module; a processing module; a housing configured to be implanted on or within a ventricle of the heart, wherein the housing encloses the stimulation module, the sensing module, and the processing module; and a first electrode electrically coupled to the sensing module and the stimulation module; and a sensing extension extending from the housing and comprising: a body extending from the housing; and a second electrode carried by the body and electrically connected to the sensing module and the stimulation module, wherein the sensing module is configured to sense electrical activity of the ventricle via the first and second electrodes, and the stimulation module is configured to deliver pacing pulses to the ventricle via at least the first electrode; and another implantable medical device configured to: sense an intrinsic depolarization of the other chamber of the heart of the patient, and in response to the intrinsic depolarization of the other chamber, deliver an electrical pulse, and characterized in that the sensing module of the leadless pacing device is configured to detect the electrical pulse delivered by the other implantable medical device via the first electrode and the second electrode, and, in response to the sensing module of the leadless pacing device detecting the electrical pulse delivered by the other implantable medical device, the processing module of the leadless pacing device is configured to control the stimulation module of the leadless pacing device to generate a pacing pulse for delivery to the ventricle via at least the first electrode in coordination with the intrinsic depolarization of the other chamber. sense an intrinsic depolarization of the other chamber of the heart of the patient, and in response to the intrinsic depolarization of the other chamber, deliver an electrical pulse, and characterized in that the sensing module of the leadless pacing device is configured to detect the electrical pulse delivered by the other implantable medical device via the first electrode and the second electrode, and, in response to the sensing module of the leadless pacing device detecting the electrical pulse delivered by the other implantable medical device, the processing module of the leadless pacing device is configured to control the stimulation module of the leadless pacing device to generate a pacing pulse for delivery to the ventricle via at least the first electrode in coordination with the intrinsic depolarization of the other chamber.