Queensland is Australia's hotspot for cardiovascular disease (CVD). Critically, beyond modifiable lifestyle risk factors; socio-demographic differences and environmental factors account for significant variations in healthcare use and outcomes among cardiac patients across the country. To better understand the impacts of these factors on the health of cardiac patients, there is a need for a comprehensive and robust longitudinal cohort study that can unpack the underlying dynamics. This paper describes the protocol for the Queensland Cardiovascular Linkage (QCard) Study. The QCard is a longitudinal linkage cohort study of cardiac patients who were first hospitalised with any cardiac condition in 2010, with follow up hospitalisations until December 2015. The primary aim of the QCard is to identify and characterise the nature and impact of socio-demographic inequality among those presenting for the first time with the most common form of CVD in Australia (heart disease) in Queensland from 2010 with minimum 5-years follow-up of subsequent healthcare utilisation and outcomes. A secondary aim is to undertake an exploration of the impact of environmental and specific health service factors on healthcare use and survival time in the same QCard cohort. Administrative public and private hospital inpatient, outpatient and emergency department data for all of Queensland will be linked with individual primary care data and pharmaceutical data. These data will also be linked to regional socio-demographic data and environmental data, as well as data that describes the features of each hospital in the region. The findings from the study will provide critical information for cardiac patients, clinicians and health policymakers. Such information ranges from identifying most vulnerable cardiac patients who may require targeted needs to providing estimates for cost-effective ways of evaluating healthcare interventions that seek to improve the health of cardiac patients.