Monitoring of dynamic changes in carotid arterial diameter, which convey information such as blood pressure and pulse, is valuable for the prevention and screening of cardiovascular diseases. Ultrasound has become an effective method due to its non-invasive sensing and high penetration. In this work, an aluminum nitride (AlN) based piezoelectric micromachined ultrasound transducer (PMUT) array is proposed and fabricated. We start with investigating the effect of different PMUT membrane radii on sensitivity and resonant frequency. Based on Micro-Electro-Mechanical System (MEMS) technology, a 13 × 14 PMUT array is fabricated within a chip area of 4 × 4 mm2 and then encapsulated by Ecoflex-30. The resonant frequency of the fabricated PMUT array is 4.3 MHz, and its sensitivity is 50 nm/V. In vivo dynamic measurements of carotid arterial diameter are carried out by putting the device on the neck of a volunteer. The amplitude of the waveform is around 1 mm, and its shape and amplitude are consistent with previous reports. The main features of the carotid pulse, including systolic upstroke, systolic decline, dicrotic notch, and diastolic runoff, are captured. This work demonstrates the potential of PMUT devices for noninvasive monitoring of the cardiovascular system.