Optimizing cardiac preload based on measured pulmonary artery pressure involves varying, for each repetition of an acute burst protocol, a parameter of pacing applied to a patient's heart during the acute burst protocol. Pulmonary artery pressure is measured during the repetitions of the acute burst protocol. The length of the repetitions is chosen so that the patient's baroreflex system does not adjust to the varied parameter of pacing during the repetitions of the acute burst protocol. An optimum ventricular preload is determined based on the measured pulmonary artery pressure. Pacing therapy is provided using a value of the parameter that is selected based on the determination of optimum ventricular preload.
