A dynamic pacemaker system for artificially pacing a patient's heart, comprising: a musculoskeletal activity sensor for detecting a rhythmic musculoskeletal activity of a patient; an implantable electrical lead connectable to a heart of the patient; an implantable ECG sensor coupled to the electrical lead for monitoring an electrical activity of the heart; an implantable pulse generator coupled to the electrical lead and configured with the electrical lead to electrically stimulate the heart in accordance with a pacing signal; and an implantable processor electrically coupled to receive signals from the ECG sensor and musculoskeletal activity sensor and configured to output the pacing signal to the pulse generator, wherein the processor is configured to: detect a recurrent aspect of the rhythmic musculoskeletal activity of the patient based on signals received from the musculoskeletal activity sensor, the detected recurrent aspect of the rhythmic musculoskeletal activity having a consistent timing relationship with a maximal musculoskeletal blood pumping; determine a frequency of the rhythmic musculoskeletal activity; identify an intrinsic heartrate of the patient based on signals received from the ECG sensor; compare the intrinsic heartrate to a target heartrate; and if the intrinsic heartrate is less than the target heartrate, provide the pacing signal to the heart at the frequency of the rhythmic musculoskeletal activity, wherein: the pacing signal causes heart contractions in a cardiac cycle to occur with a predominantly constant timing relationship with respect to the detected recurrent aspect of the rhythmic musculoskeletal activity, and the pacing signal results in the maximal musculoskeletal pumping occurring predominantly within a diastolic period of the cardiac cycle. a musculoskeletal activity sensor for detecting a rhythmic musculoskeletal activity of a patient; an implantable electrical lead connectable to a heart of the patient; an implantable ECG sensor coupled to the electrical lead for monitoring an electrical activity of the heart; an implantable pulse generator coupled to the electrical lead and configured with the electrical lead to electrically stimulate the heart in accordance with a pacing signal; and an implantable processor electrically coupled to receive signals from the ECG sensor and musculoskeletal activity sensor and configured to output the pacing signal to the pulse generator, wherein the processor is configured to: detect a recurrent aspect of the rhythmic musculoskeletal activity of the patient based on signals received from the musculoskeletal activity sensor, the detected recurrent aspect of the rhythmic musculoskeletal activity having a consistent timing relationship with a maximal musculoskeletal blood pumping; determine a frequency of the rhythmic musculoskeletal activity; identify an intrinsic heartrate of the patient based on signals received from the ECG sensor; compare the intrinsic heartrate to a target heartrate; and if the intrinsic heartrate is less than the target heartrate, provide the pacing signal to the heart at the frequency of the rhythmic musculoskeletal activity, wherein: the pacing signal causes heart contractions in a cardiac cycle to occur with a predominantly constant timing relationship with respect to the detected recurrent aspect of the rhythmic musculoskeletal activity, and the pacing signal results in the maximal musculoskeletal pumping occurring predominantly within a diastolic period of the cardiac cycle. detect a recurrent aspect of the rhythmic musculoskeletal activity of the patient based on signals received from the musculoskeletal activity sensor, the detected recurrent aspect of the rhythmic musculoskeletal activity having a consistent timing relationship with a maximal musculoskeletal blood pumping; determine a frequency of the rhythmic musculoskeletal activity; identify an intrinsic heartrate of the patient based on signals received from the ECG sensor; compare the intrinsic heartrate to a target heartrate; and if the intrinsic heartrate is less than the target heartrate, provide the pacing signal to the heart at the frequency of the rhythmic musculoskeletal activity, wherein: the pacing signal causes heart contractions in a cardiac cycle to occur with a predominantly constant timing relationship with respect to the detected recurrent aspect of the rhythmic musculoskeletal activity, and the pacing signal results in the maximal musculoskeletal pumping occurring predominantly within a diastolic period of the cardiac cycle. the pacing signal causes heart contractions in a cardiac cycle to occur with a predominantly constant timing relationship with respect to the detected recurrent aspect of the rhythmic musculoskeletal activity, and the pacing signal results in the maximal musculoskeletal pumping occurring predominantly within a diastolic period of the cardiac cycle.