Measurement of cardiorespiratory fitness (VO2max) is considered an important tool in risk prediction of cardiovascular disease and overall patient management. The gold standard method for determining VO2max is a maximal cardiopulmonary exercise test (CPET). This requires time, maximal exercise until voluntary exhaustion and expensive equipment and are therefor not always suitable. A non-exercise VO2max prediction model using seismocardiography (SCG) at rest in combination with demographic data has been proposed as an possible alternative. SCG is a non-invasive three-dimensional measurement technique of precordial vibrations caused by the beating heart and can provide information on cardiac performance. New advances in low-weight three-axis accelerometer, signal processing and feature selection has made this methodology attractive in the recent years. VentriJect Aps has develop a medical device for measuring SCG (SeismoFit) together with an cloud solution for signal processing and prediction of VO2max. The validity of the SeismoFit device has previously been assesses in healthy subjects, but not yet in patients. The aim of this study is therefore to investigate the validity of the SeismoFit VO2max estimation in patients with heart failure (HF) or ischemic heart disease (IHD).