Negative affectivity has been defined as a predisposition to experience intense states of negative emotions. As a trait concept it is a dimension that reflects stable and pervasive differences in negative mood and self-concept. There has been systematic evidence linking negative affectivity to anxiety, depression, psychosomatic complaints, pain symptoms, and adherence to life style changes. Several studies have demonstrated a link between negative affectivity and quality of life. However, as the majority of these studies have been cross-sectional, it has been difficult to establish causal relations between quality of life and negative affect. The present study is a longitudinal investigation of negative affectivity and quality of life in patients undergoing coronary artery bypass grafting (N = 157). Negative affectivity and quality of life were assessed with the Positive and Negative Affect Schedule (PANAS) and with the MacNew Quality of Life after Myocardial Infarction Questionnaire (MacNew QLMI) on admission day, one, and six months after the operation. Causal and reciprocal relationships were tested using a cross-lagged designs analysis via structural equation modeling. Results indicated that the causal model represented the best fit to the data. Results of the study are discussed in terms of the clinical importance of identifying patients at risk of experiencing severe restrictions in their quality of life.