An apparatus for treating a patient's heart, comprising: a sensor for measuring hemodynamics of the heart; and a processing unit which receives the hemodynamics from the sensor and uses the hemodynamics to determine whether to shock the heart, pace the heart, or observe the heart and offer no therapy, wherein the processing unit is configured to: determine hemodynamics of the heart from a real part and an imaginary part of impedance of the heart as measured by the sensor; determine the heart's myocardium and blood component; determine volume in regard to the heart from the blood component to identify current stroke volume of the heart; compare the current stroke volume to a baseline stroke volume, and if the current stroke volume is below the average stroke volume by at least a predetermined amount, produce a shock signal to shock the heart; wherein the processing unit is configured to cause no action when the current stroke volume is approximately 80% to 100% of baseline stroke volume; wherein the processing unit is configured to increase the sensing frequency of the stroke volume when the current stroke volume is approximately between 60% to 80% of baseline stroke volume; wherein the processing unit configured to review the patient's ECG and to send a shock signal to shock the heart when the current stroke volume is between about 40% to 60% of baseline stroke file; and wherein the processing unit configured to send a shock signal to shock the heart when the current stroke volume is between approximately 0% to 40% of baseline stroke volume. a sensor for measuring hemodynamics of the heart; and a processing unit which receives the hemodynamics from the sensor and uses the hemodynamics to determine whether to shock the heart, pace the heart, or observe the heart and offer no therapy, wherein the processing unit is configured to: determine hemodynamics of the heart from a real part and an imaginary part of impedance of the heart as measured by the sensor; determine the heart's myocardium and blood component; determine volume in regard to the heart from the blood component to identify current stroke volume of the heart; compare the current stroke volume to a baseline stroke volume, and if the current stroke volume is below the average stroke volume by at least a predetermined amount, produce a shock signal to shock the heart; wherein the processing unit is configured to cause no action when the current stroke volume is approximately 80% to 100% of baseline stroke volume; wherein the processing unit is configured to increase the sensing frequency of the stroke volume when the current stroke volume is approximately between 60% to 80% of baseline stroke volume; wherein the processing unit configured to review the patient's ECG and to send a shock signal to shock the heart when the current stroke volume is between about 40% to 60% of baseline stroke file; and wherein the processing unit configured to send a shock signal to shock the heart when the current stroke volume is between approximately 0% to 40% of baseline stroke volume. determine hemodynamics of the heart from a real part and an imaginary part of impedance of the heart as measured by the sensor; determine the heart's myocardium and blood component; determine volume in regard to the heart from the blood component to identify current stroke volume of the heart; compare the current stroke volume to a baseline stroke volume, and if the current stroke volume is below the average stroke volume by at least a predetermined amount, produce a shock signal to shock the heart; wherein the processing unit is configured to cause no action when the current stroke volume is approximately 80% to 100% of baseline stroke volume; wherein the processing unit is configured to increase the sensing frequency of the stroke volume when the current stroke volume is approximately between 60% to 80% of baseline stroke volume; wherein the processing unit configured to review the patient's ECG and to send a shock signal to shock the heart when the current stroke volume is between about 40% to 60% of baseline stroke file; and wherein the processing unit configured to send a shock signal to shock the heart when the current stroke volume is between approximately 0% to 40% of baseline stroke volume.