A medical-device system, comprising: a signal receiver circuit configured to receive exertion information of a subject and cardiac acceleration information of the subject, wherein the cardiac acceleration information includes information indicative of third heart sound, S3; and an assessment circuit configured to determine a change in cardiac acceleration information of the subject at exertion relative to cardiac acceleration information of the subject at rest, and to determine an indication of heart failure with preserved ejection fraction, HFpEF, of the subject using the determined change in cardiac acceleration information, wherein the assessment circuit is configured to: determine a period of rest of the subject using the received exertion information; determine a period of exertion of the subject using the received exertion information; determine a measure of cardiac acceleration information of the subject for the determined period of rest; and determine a measure of cardiac acceleration information of the subject for the determined period of exertion, wherein the determined measure of cardiac acceleration information is, in each case, one or more of magnitude or energy of S3, or a ratio of magnitude or energy of S3 and of one of first heart sound, S1, or second heart sound, S2, or fourth heart sound, S4, and wherein, to determine the change in cardiac acceleration information of the subject at exertion relative to cardiac acceleration information relative to rest, the assessment circuit is configured to determine a change in the determined measure of cardiac acceleration information of the subject for the determined period of exertion relative to the determined measure of cardiac acceleration information of the subject for the determined period of rest, and wherein the assessment circuit is configured to determine the indication of HFpEF using the determined change in the determined measure of cardiac acceleration information of the subject for the determined period of exertion relative to the determined measure of cardiac acceleration information of the subject for the determined period of rest. a signal receiver circuit configured to receive exertion information of a subject and cardiac acceleration information of the subject, wherein the cardiac acceleration information includes information indicative of third heart sound, S3; and an assessment circuit configured to determine a change in cardiac acceleration information of the subject at exertion relative to cardiac acceleration information of the subject at rest, and to determine an indication of heart failure with preserved ejection fraction, HFpEF, of the subject using the determined change in cardiac acceleration information, wherein the assessment circuit is configured to: determine a period of rest of the subject using the received exertion information; determine a period of exertion of the subject using the received exertion information; determine a measure of cardiac acceleration information of the subject for the determined period of rest; and determine a measure of cardiac acceleration information of the subject for the determined period of exertion, determine a period of rest of the subject using the received exertion information; determine a period of exertion of the subject using the received exertion information; determine a measure of cardiac acceleration information of the subject for the determined period of rest; and determine a measure of cardiac acceleration information of the subject for the determined period of exertion, wherein the determined measure of cardiac acceleration information is, in each case, one or more of magnitude or energy of S3, or a ratio of magnitude or energy of S3 and of one of first heart sound, S1, or second heart sound, S2, or fourth heart sound, S4, and wherein, to determine the change in cardiac acceleration information of the subject at exertion relative to cardiac acceleration information relative to rest, the assessment circuit is configured to determine a change in the determined measure of cardiac acceleration information of the subject for the determined period of exertion relative to the determined measure of cardiac acceleration information of the subject for the determined period of rest, and wherein the assessment circuit is configured to determine the indication of HFpEF using the determined change in the determined measure of cardiac acceleration information of the subject for the determined period of exertion relative to the determined measure of cardiac acceleration information of the subject for the determined period of rest.