An apparatus for noninvasively determining a cause of a blood pressure change, comprising: an input port configured to receive heart sounds; a processor configured to perform a method of noninvasively determining a cause of a blood pressure change; a memory configured to store a computer program by which noninvasively determining the cause of the blood pressure change is implemented; and an output port configured to output information about the determined cause of the blood pressure change, characterized in that the processor is configured to obtain a first maximum amplitude of a first heart sound and a second maximum amplitude of a second heart sound, from the received heart sounds, to monitor a first change in the first maximum amplitude and a second change in the second maximum amplitude, to estimate a first change amount of a first index on a myocardial contractile force, a second change amount of a second index on the myocardial contractile force, and a third change amount of a third index on vascular resistance, based on increasing or decreasing of a blood pressure of the patient, a first change amount of the first maximum amplitude, and a second change amount of the second maximum amplitude of the second heart sound, and to determe the cause of the blood pressure change of the patient as an effect of at least one of alpha action, alpha blockage, beta action and beta blockage, based on results of the estimation of the first change amount of the first index, the second change amount of the second index and the third change amount of the third index, wherein the first heart sound corresponds to a closed sound of a mitral valve or a tricuspid valve, and the second heart sound corresponds to a closed sound of an aortic valve or a pulmonary valve. an input port configured to receive heart sounds; a processor configured to perform a method of noninvasively determining a cause of a blood pressure change; a memory configured to store a computer program by which noninvasively determining the cause of the blood pressure change is implemented; and an output port configured to output information about the determined cause of the blood pressure change, characterized in that the processor is configured to obtain a first maximum amplitude of a first heart sound and a second maximum amplitude of a second heart sound, from the received heart sounds, to monitor a first change in the first maximum amplitude and a second change in the second maximum amplitude, to estimate a first change amount of a first index on a myocardial contractile force, a second change amount of a second index on the myocardial contractile force, and a third change amount of a third index on vascular resistance, based on increasing or decreasing of a blood pressure of the patient, a first change amount of the first maximum amplitude, and a second change amount of the second maximum amplitude of the second heart sound, and to determe the cause of the blood pressure change of the patient as an effect of at least one of alpha action, alpha blockage, beta action and beta blockage, based on results of the estimation of the first change amount of the first index, the second change amount of the second index and the third change amount of the third index, wherein the first heart sound corresponds to a closed sound of a mitral valve or a tricuspid valve, and the second heart sound corresponds to a closed sound of an aortic valve or a pulmonary valve. <EOS>