Seizure-like episodes may occasionally arise from cardiovascular causes rather than primary neurological disease, leading to diagnostic delay. We report an adolescent girl who presented with recurrent generalised tonic episodes with cyanosis and transient loss of consciousness. Initial evaluation for epilepsy, including video electroencephalography during an event, was unremarkable. Cardiac assessment revealed marked biatrial dilatation with restrictive ventricular physiology on echocardiography, consistent with restrictive cardiomyopathy (RCM). Ambulatory monitoring documented atrial tachycardia (AT) immediately preceding the episodes, strongly suggesting arrhythmia-related cerebral hypoperfusion as the underlying mechanism of convulsive syncope. The patient subsequently experienced cardiac arrest but was successfully resuscitated and stabilised with rhythm control therapy. Genetic testing identified a heterozygous TNNI3 variant consistent with familial RCM. This case highlights the importance of considering cardiac causes in apparent seizures, illustrates the haemodynamic vulnerability of RCM to AT and underscores the value of early cardiac evaluation in children with unexplained seizure-like events.