When COVID-19 first emerged, it was assumed that the virus induces only lung disease, but more and more studies have shown that the whole body gets affected.
Cardiovascular disease is a common condition in patients with severe COVID-19 and is considered to increase in-hospital mortality rate.  In one study, covering 416 hospitalized COVID-19 patients, 20% showed cardiac injury.  Another study of 36 severe COVID-19 cases (all patients were admitted to the ICU) showed that 44% had arrhythmia. 
Notably, the virus affects also the blood itself. Respiratory viruses, in general, have been shown to activate coagulation and SARS-CoV-2 doesn’t seem to be an exception. Blood clots can lead to pulmonary embolism or stroke and finally can be fatal.  One study found that out of 184 COVID-19 patients admitted to the ICU, 31% showed thrombotic complications, despite systematic thrombosis prophylaxis.  Autopsies on 12 patients with COVID-19 showed deep vein thrombosis in seven patients whereof four had pulmonary embolism (PE) as main pathological findings. In two of these cases, PE was directly stated in the clinical cause of death.  The impact of dissaminated intravascular coagulation affects especially patients with underlying conditions such as vascular disease. The virus’s ability to attack blood vessels explains why not only patients with lung disease are at high risk, but also individuals with vascular diseases, such as diabetes and high blood pressure.
The autopsies also revealed viremia in 6 of 10 patients . The exact mechanisms how SARS-CoV-2 attacks the cardiovascular system is still unknown. Both heart and blood have high amounts of Angiotensin-converting enzyme 2 (ACE2), the protein used by SARS-CoV-2 as a viral receptor for cell-entry, suggesting direct infection with the virus. 
Meanwhile a study focusing on ACE2 as target for treating SARS-CoV-2 infections proved the infection of engineered human blood vessel tissues . However, secondary reasons, such as lack of oxygen due to lung damage or cytokine storm can also be potential causes.
Rather than performing systemic thrombosis prophylaxis by treating all hospitalized COVID-19 patients with anticoagulation drugs, it is advised that physicians should closely monitor signs of thrombotic complications and order appropriate diagnostic tests. 
Studies on SARS-CoV-2 revealed a high correlation between severity and outcome of COVID-19 in patients with increased D-Dimer levels, which is a parameter for detection of thrombotic diseases and microthrombotic events. [8, 9, 10] The determination of serum D-Dimer levels is even strongly suggested by the IFCC. 
- Mehra M, et al. Cardiovascular disease, drug therapy, and mortality in COVID-19. New England Journal of Medicine (2020).
- Shi S, et al. Association of cardiac injury with mortality in hospitalized patients with COVID-19 in Wuhan, China. JAMA cardiology (2020).
- Wang D, et al. Clinical characteristics of 138 hospitalized patients with 2019 novel coronavirus–infected pneumonia in Wuhan, China. Jama 323.11 (2020): 1061-1069.
- Van Wissen M, et al. Acute respiratory tract infection leads to procoagulant changes in human subjects. Journal of Thrombosis and Haemostasis 9.7 (2011): 1432.
- Klok FA, et al. Incidence of thrombotic complications in critically ill ICU patients with COVID-19. Thrombosis research (2020).
- Wichmann D, et al. Autopsy findings and venous thromboembolism in patients with COVID-19: a prospective cohort study. Annals of internal medicine (2020).
- Monteil V, et al. Inhibition of SARS-CoV-2 infections in engineered human tissues using clinical-grade soluble human ACE2. Cell (2020).
- Lippi G, et al. Thrombocytopenia is associated with severe coronavirus disease 2019 (COVID-19) infections: A meta-analysis. Clinica Chimica Acta. 2020;506:145–8.
- Tang N, et al. Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia. J Thromb Haemost. 2020;18:844–7.
- Lippi G, Favaloro EJ. D-dimer is Associated with Severity of Coronavirus Disease 2019: A Pooled Analysis. Thromb Haemost. 2020;s-0040-1709650.
- IFCC Information Guide on COVID-19 [Internet]. IFCC Information Guide on COVID-19. 2020. Available from: www.ifcc.org/ifcc-news/2020-03-26-ifcc-information-guide-on-covid-19/