ABSTRACT Identification of novel modifiable factors associated with cardiac remodeling may lead to new therapeutic approaches and opportunities for early prevention of heart failure. We recently reported from data observed in the Cardiovascular Health Study (CHS), a prospective study of older adults, that plasma ceramides (Cer) and sphingomyelins (SM) were associated with risk of incident heart failure, but the associations of Cer and SM species with the saturated fatty acid 16:0 (16 carbons:0 double bond) differed from the associations of species with the fatty acids 20:0, 22:0 or 24:0. The main objectives of this current application are to probe the mechanistic underpinnings of the observed association of Cer and SM with heart failure. Specifically, we aim to examine whether plasma Cer and SM species with the fatty acids 16:0, 20:0, 22:0 and 24:0 are associated with changes over time in cardiac imaging measures of hypertrophy (Aim 1a); and to examine the associations of Cer and SM species with cardiac imaging measures of fibrosis (Aim 1b). Furthermore, we will determine metabolic and transcriptional effects of altering levels of Cer and SM species in primary human ventricular cardiomyocytes (Aim 2). We will extend the CHS findings on Cer and SM and heart failure to four race/ethnic groups in MESA (Multi-Ethnic Study of Atherosclerosis), and we will gain evidence of causality using Mendelian Randomization analyses (Aim 3). In addition, we will identify life-style and other factors that influence changes in Cer and SM levels over time using repeat measurements, to gain information for future prevention efforts (Aim 4). To address the study aims, we will measure Cer and SM in 5,000 existing plasma samples in MESA, including 4000 baseline samples and 1000 repeats; we will use existing Cer and SM measurements in CHS and obtain new Cer and SM measurements in 1000 samples in CHS; and we will conduct targeted experiments in cardiomyocytes. The study will take advantage of existing, high quality cardiac magnetic resonance (CMR) data at two time points, and gadolinium enhanced CMR imaging in MESA; existing Cer and SM data at one time point in CHS; follow-up information, genetics data and extensive covariate data in both MESA and CHS. This comprehensive project leverages two large, independent cohorts and targeted in vitro experimentation in human cardiomyocytes to systematically define and validate the role of Cer and SM in the progression to heart failure. Its successful completion will bring new insights into mechanisms and processes critical in the early stages of cardiac failure and can help direct future novel drug targets and prevention efforts.