An implantable heart monitoring device comprising: at least one memory; and a control circuit configured to communicate with a plurality of implanted electrode members (21, 22, 31, 32, 41, 42, 43) adapted to be positioned in a heart or in relation to a heart of a living being such that the control circuit, by means of said implanted electrode members (21, 22, 31, 32, 41, 42, 43), is able to detect the heart rate of said living being and to derive information correlated to the stroke volume of said heart, wherein the control circuit is configured to be able to carry out the following steps: a) detect the heart rate, b) derive said information correlated to the stroke volume at said detected heart rate, and c) store the detected heart rate and the derived information correlated to the stroke volume in said memory, wherein said control circuit is configured to automatically carry out steps a) to c) at a plurality of different occasions at different, naturally varying, heart rates, such that said memory comprises information that indicates the stroke volume as a function of the heart rate, wherein the control circuit is configured to derive said information correlated to the stroke volume at said detected heart rate by carrying out an impedance measurement that indicates how the amount of blood in the left ventricle of the heart varies with time, which measurement thus creates a signal that varies with time, and thereby constitutes a curve that indicates how the amount of blood in the left ventricle of the heart varies with time; characterized in that the control circuit is configured to be able to determine whether the contraction of the ventricle at the occasion in question belongs to normal sinus rhythm or a premature ventricular contraction, and if the contraction of the ventricle belongs to PVC, then the control circuit is configured to store the derived information separately in said memory such that the memory contains information that the derived information relates to PVC such that the stored information in the memory is distinguished from the information obtained when the contraction is due to normal sinus rhythm; and the control circuit is configured to create a warning message if the stored derived information relating to PVC indicates that the stroke volume decreases more than a predetermined amount when the heart rate increases. at least one memory; and a control circuit configured to communicate with a plurality of implanted electrode members (21, 22, 31, 32, 41, 42, 43) adapted to be positioned in a heart or in relation to a heart of a living being such that the control circuit, by means of said implanted electrode members (21, 22, 31, 32, 41, 42, 43), is able to detect the heart rate of said living being and to derive information correlated to the stroke volume of said heart, wherein the control circuit is configured to be able to carry out the following steps: a) detect the heart rate, b) derive said information correlated to the stroke volume at said detected heart rate, and c) store the detected heart rate and the derived information correlated to the stroke volume in said memory, wherein said control circuit is configured to automatically carry out steps a) to c) at a plurality of different occasions at different, naturally varying, heart rates, such that said memory comprises information that indicates the stroke volume as a function of the heart rate, wherein a) detect the heart rate, b) derive said information correlated to the stroke volume at said detected heart rate, and c) store the detected heart rate and the derived information correlated to the stroke volume in said memory, wherein said control circuit is configured to automatically carry out steps a) to c) at a plurality of different occasions at different, naturally varying, heart rates, such that said memory comprises information that indicates the stroke volume as a function of the heart rate, wherein the control circuit is configured to derive said information correlated to the stroke volume at said detected heart rate by carrying out an impedance measurement that indicates how the amount of blood in the left ventricle of the heart varies with time, which measurement thus creates a signal that varies with time, and thereby constitutes a curve that indicates how the amount of blood in the left ventricle of the heart varies with time; characterized in that the control circuit is configured to be able to determine whether the contraction of the ventricle at the occasion in question belongs to normal sinus rhythm or a premature ventricular contraction, and if the contraction of the ventricle belongs to PVC, then the control circuit is configured to store the derived information separately in said memory such that the memory contains information that the derived information relates to PVC such that the stored information in the memory is distinguished from the information obtained when the contraction is due to normal sinus rhythm; and the control circuit is configured to create a warning message if the stored derived information relating to PVC indicates that the stroke volume decreases more than a predetermined amount when the heart rate increases.