There is provided an ambulatory system, comprising at least first and second wearable sensors, for determining pulse transit time (PTT) between at least a first and at least a second fixed location within the cardiovascular system of a subject. The system comprises at least a first device, wherein the first device can contact the skin of the subject, the first device being positioned proximate to the first fixed location； and also comprises at least a second device, wherein the second device can contact the skin of the subject, the second device being positioned proximate to the second fixed location. The system further comprises a data collection module that is in communication with the first and second devices. The first device is configured to detect a timing cue within the cardiac cycle of the subject, and the second device is configured to detect a pulse pressure wave passing through the second fixed location. The data collection module collects data relating to the transition of the pulse pressure wave passing through the second fixed location, thereby enabling determination of a pulse transit time (PTT) between the first and second fixed locations.
