A method is proposed for investigation of or ascertaining pulse or heartbeat. The method first comprises directing illuminating radiation to illuminate a body part such as a finger. The illuminating radiation is of a wavelength or wavelength band substantially in the blue light region of the light spectrum. Then, an optical speckle pattern of the illuminated body part resulting from the illumination of the body part is obtained and imaged. The optical speckle pattern is representative of the heartbeat and by correlation of frames extracted from the speckle pattern, the pulse or beat extent of the body part may be ascertained.