A pressure sensor (400, 500, 600) for measuring the heart rate of a patient comprising: a substrate (420, 620) having a top (421, 621) and a bottom surface; a first housing (450, 650) defining a gas-filled interior cavity arranged on the substrate (420, 620), the housing comprising a body portion comprising a peripheral wall, the housing (450, 650) having a first end and a second end; an elastic sealing element (480, 580, 680) attached to the second end of the first housing (450, 550, 650) and generally covering an open end of the interior cavity for sealing the interior cavity with respect to an external environment, wherein a portion (481, 581, 681) of the elastic sealing element (480, 580, 680) is configured to be placed in contact with a patient and moveable in response to a pressure acting thereon, the elastic sealing element comprising (i) an arcuate portion (481, 681) that protrudes away from the cavity space in an unbiased state or (ii) a protrusion extending from an exposed side of the elastic sealing element in a direction away from the interior cavity; and a semiconductor die (410, 610) arranged on the substrate (420, 620) and defining a pressure sensing diaphragm (412, 612) exposed to the gas occupying the interior cavity, wherein the semiconductor die comprises a plurality of piezo-electric resistive elements configured to detect diaphragm strain; and signal conditioning circuitry is provided on the substrate to generate a value indicative of a heart rate of a patient, characterised in that: the pressure sensor further comprises a mechanical stop (454, 620) arranged between the moveable portion (481, 681) of the elastic sealing element (480, 680) and the semiconductor die (410, 610) thereby to limit excessive travel of the elastic sealing element (480, 580, 680) thereby to protect the semiconductor die (410, 610) from damage. a substrate (420, 620) having a top (421, 621) and a bottom surface; a first housing (450, 650) defining a gas-filled interior cavity arranged on the substrate (420, 620), the housing comprising a body portion comprising a peripheral wall, the housing (450, 650) having a first end and a second end; an elastic sealing element (480, 580, 680) attached to the second end of the first housing (450, 550, 650) and generally covering an open end of the interior cavity for sealing the interior cavity with respect to an external environment, wherein a portion (481, 581, 681) of the elastic sealing element (480, 580, 680) is configured to be placed in contact with a patient and moveable in response to a pressure acting thereon, the elastic sealing element comprising (i) an arcuate portion (481, 681) that protrudes away from the cavity space in an unbiased state or (ii) a protrusion extending from an exposed side of the elastic sealing element in a direction away from the interior cavity; and a semiconductor die (410, 610) arranged on the substrate (420, 620) and defining a pressure sensing diaphragm (412, 612) exposed to the gas occupying the interior cavity, wherein the semiconductor die comprises a plurality of piezo-electric resistive elements configured to detect diaphragm strain; and signal conditioning circuitry is provided on the substrate to generate a value indicative of a heart rate of a patient, characterised in that: the pressure sensor further comprises a mechanical stop (454, 620) arranged between the moveable portion (481, 681) of the elastic sealing element (480, 680) and the semiconductor die (410, 610) thereby to limit excessive travel of the elastic sealing element (480, 580, 680) thereby to protect the semiconductor die (410, 610) from damage.