Myocarditis refers to inflammation of the myocardium with incidence ranging from 1 to 9% in routine autopsies and about 5–12% in autopsy cases of sudden cardiac death. Based on the clinical and pathologic manifestations, myocarditis is divided into four groups: fulminant, acute, chronic active, and chronic [4, 14]. Myocarditis presents with an extended range of symptoms and is often non-diagnosed underlying etiology of chronic dilated cardiomyopathy and acute heart failure, leading to sudden death [15]. Definitive diagnosis of myocarditis is by histology. Myocarditis presents with wide range of symptoms ranging from mild dyspnea or chest pain subsiding without specific treatment, dyspnea, palpitations, fatigue, dizziness, or syncope to even cardiogenic shock leading to death. Dilated cardiomyopathy with chronic heart failure is a long-term sequela of myocarditis [15]. Acute myocarditis mimics an ACS on initial presentation with elevated troponin, abnormal ECGs including ST segment elevation, AV block, supraventricular or ventricular arrhythmia, and echocardiography often showing preserved left ventricular function; except in severe cases, mild regional dysfunction/localized wall motion abnormalities (WMAs) can be seen; thus, diagnosis of myocarditis becomes challenging and is often a disease of exclusion from other cardiac pathologies, because of non-specificity in presentation [2, 4]. The most frequent cause of myocarditis is viral infections, but other infectious pathogens such as fungi, bacteria, protozoans, as well as toxins hypersensitivity drug reactions, giant-cell myocarditis, autoimmune diseases, and sarcoidosis can also cause myocarditis [1, 15]. In patients with suspected myocarditis, echocardiography, mainly transthoracic echocardiography (TTE) and CMR, serves as standard noninvasive imaging modality which preclude invasive procedures such as endomyocardial biopsy and coronary angiography. Nuclear imaging has been less sensitive to diagnose myocarditis [3, 4].

Due to its high spatial resolution and with just different protocol components—steady-state free precession; T2-weighted triple inversion recovery; and phase-sensitive inversion-recovery gradient echo (early and delayed Gd enhancement), cardiovascular MRI gives detailed information on myocardial tissue characteristics, even subtle, patchy areas of in vivo inflammatory hyperemia, edema, necrosis/fibrosis (Lake Louise Criteria for Acute Myocarditis); contractile dysfunction, and accompanying pericardial effusion [3, 16]. CMR can distinguish between variable causative etiologies like myocarditis, acute infarction, and other cardiomyopathies. Thus, delayed CMR is known as the gold standard for differentiating acute non-ischemic myocardial injury and in vivo detection of scarring associated with myocardial infarction [17] and also helps in evaluating the myocarditis’s activity and severity. The conventional findings of myocarditis are delayed epicardial enhancement and sparing the subendocardium, with non-segmental distribution. Therefore, delayed CMR provides comprehensive and early diagnosis in patients with suspected myocarditis, thus aiding in appropriate treatment and also in cases of follow-up [3, 16]. Thus, CMR has better accuracy in detecting subtle changes compared to TTE which helps in assessing the functional injury [4]. Varied illicit and licit drugs like anticonvulsants, antipsychotics, antibiotics, alcohol, amphetamines, and cannabis have been implicated as causes of myocarditis [18]. Cannabis sativa commonly known as Marijuana is one of the most used recreational drugs and the most abused illicit substance in India and the world [5]. As per Ministry of Social Justice and Empowerment’s survey conducted to understand the magnitude of substance use in India, 2.83% or 31 million people aged 10–70 years were found to be actively consuming cannabis products in 2019 [19]. Despite few studies stating the medical use of marijuana in treatment of neuropathic pain and certain cannabinoids in treating nausea and vomiting from cancer chemotherapy, the abuse of marijuana has been associated with adverse psychiatric, neurological, respiratory, gastrointestinal and cardiovascular effects [20]. Two of the major active cannabinoids in marijuana are tetrahydrocannabinol (THC) and cannabidiol (CBD), which act through various widely spread CB receptors in the body [6]. Marijuana shows cardiovascular adverse effects by marijuana, which are mainly caused via action of THC on CB1 receptors present in myocytes and range from rhythm and rate irregularities (like tachycardia and arrhythmias), blood pressure changes (like hypotension or hypertension), atherosclerosis, vasospasm (leading to acute coronary syndrome), vasodilation, myocardial infarction, coronary dissection, myopericarditis to cardiomyopathy leading to cardiac death [6, 7, 21]. The exact mechanism responsible for the myocarditis is unclear; however, presence of adulterants or contaminants like heavy metals and pesticides is considered a possible hypothesis [12]. Myocarditis secondary to cannabis is seen in few proven cases reported till date [8–13]. In 2008, the first case of a 29-year-old man who developed toxic myocarditis from cannabis addiction and was maintained for 96 days by a left ventricular assist device was published by Leontiadis et al. [22]. In our case, as patient presented with sudden onset of severe chest and epigastric pain, radiating to neck and left arm and associated sweating with raised troponin levels and abnormal ECG showing ST elevation, the diagnostic picture appeared to be more like ACS/ myocardial infarction. However, on further imaging findings on CMR, the diagnosis of myocarditis was made, which after detailed revaluation of clinical history was presumed to be secondary to toxin (cannabis) abuse. Thus, non-ischemic myocardial injury causes like myocarditis should be considered in young patients especially, who are presenting to emergency with symptoms mimicking ACS, and thus, CMR should be advised as the first line of diagnostic imaging tool (based on its availability) in all such cases. Although viral etiology is the most frequent cause of myocarditis, however, in a patient with negative virological markers, a detailed history pertaining to the drug use/abuse should be done and toxin-related myocarditis should be considered as a possible etiology. Also, many studies have shown the association between marijuana and myocarditis, so in our case with the history of marijuana abuse which was aided by diagnosis of myocarditis on CMR, a diagnosis of toxic myocarditis presumed secondary to marijuana/cannabis toxin abuse was considered.