An implantable medical device (IMD) may include a housing having a proximal end and a distal end and a set of one or more electrodes connected to but spaced apart from the housing. The IMD may further include a controller disposed within the housing, wherein the controller is configured to sense cardiac electrical signals, and deliver electrical stimulation pulses via the first set of one or more electrodes. In some embodiments, a first portion of the housing is configured to be disposed at least partly within a coronary sinus of a patient's heart and a second portion of the housing is configured to be disposed at least partly within a right atrium of the patient's heart.