Pacemakers and implantable defibrillators presently operate without access to hemodynamic information. If available, such data would allow more appropriate tailoring of delivered therapy according to perfusion status, optimization of device function, and enhancement of disease monitoring and management. A candidate method for hemodynamic sensing in these devices is photoplethysmography (PPG), which uses light to noninvasively detect changes in blood volume. The present study tested the hypotheses that PPG can function in a subcutaneous location, that the acute changes in blood volume it detects are directly proportional to changes in arterial pressure, and that optimum pacing intervals identified by it are concordant with those determined by arterial pressure. Aortic pressure and PPG were simultaneously recorded in 10 dogs under general anesthesia during changes in atrio-ventricular (AV) delay and bursts of rapid pacing to simulate tachy-arrhythmias. Direct proportionality between transient changes in pressure and PPG waveforms was tested using regression analysis. Correlation coefficients were 0.95 (SD 0.03) and 0.72 (SD 0.24) for rapid-pacing and AV delay protocols, respectively, with linear appearance of scatter plots. The data were well described by a directly proportional relationship. Optimum AV delays estimated from the induced changes in aortic pressure and PPG waveforms were concordant. This preliminary canine study demonstrates that photoplethysmography can function subcutaneously and that it may serve as a surrogate for acute changes in arterial pressure.